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BOARD OF TRADE


CIVIL AIRCRAFT ACCIDENT


Report on the Accident to
Boeing 727-112C YA-FAR 1.5 miles east of London (Gatwick) Airport on 5th January 1969


YA-FAR being towed onto stand 1968

LONDON: HER MAJESTY'S STATIONERY OFFICE
Price10s. 0d. [50p] net

Accident Report No. EW/C/303

ACCIDENTS INVESTIGATION BRANCH

AIRCRAFT Boeing 727 - 112C
 
  YA-FAR  
     
ENGINES Three Pratt and Whitney JT8D-7  
     
REGISTERED OWNER & OPERATOR Ariana Afghan Airlines  
     
CREW Captain R Nowroz - Commander -Seriously injured  
  First Officer A Z Attayee - Co-pilot - Seriously injured  
  Flight Engineer M H Formuly - Flight Engineer -Seriously injured  
  Ground Engineer A H Alam - Supernumary - Killed  
  Steward Hahatullah - Killed  
  Steward G Sakhi - Killed  
  Stewardess Tahera - Killed  
  Stewardess Zeinab - Killed  
     
PASSENGERS 54  -  43 Killed, 11 Seriously injured  
     
OTHERS 3  -  2 Killed, 1 Seriously injured  
     
PLACE OF ACCIDENT 1.5 miles east of Gatwick Airport, London  
     
DATE AND TIME 5 January 1969 at 0134 hrs.  
     
  Accredited Representatives from Afghanistan (State of Registry) and the United States of America (State of Manufacture) participated in the investigation.  
     
  All times in this report are G.M.T.  


Summary

The accident occurred on a scheduled passenger flight from Frankfurt when the aircraft was making an ILS approach for a night landing on Runway 27 at Gatwick Airport. The weather was clear except that freezing fog persisted in places including the Gatwick area. The runway visual range (RVR) at Gatwick was 100 metres. The approach was commenced with the autopilot coupled to the instrument landing system (ILS) but after the glide-slope had been captured the commander who was at the controls, disconnected the autopilot because the "stabiliser out of trim" warning light illuminated. At the outer marker the flap setting was changed from 1° to 30° and shortly afterwards the rate of descent increased and the aircraft descended below the glide-slope. Some 200 feet from the ground the pilot realised that the aircraft was too low and initiated a missed approach procedure. The aircraft began to respond but the descent was not arrested in time to avoid a collision with trees and a house that destroyed both the aircraft and the house and set the wreckage on fire. The report concludes that the accident was the result of the commander inadvertently allowing the aircraft to descend below the glide-slope during an approach to land until it was too low for recovery to be effected.

 

1. Investigation

1.1 History of the flight

The aircraft was on a scheduled flight (FG 701) from Kabul to Gatwick Airport, London, via Kandahar, Beirut, Istanbul and Frankfurt. At Beirut a slip crew, under Captain Nowroz, took over the aircraft for the remainder of the flight to Gatwick. The landings at Istanbul and Frankfurt were routine and the only noteworthy incident occurred at Frankfurt when the "stabilizer out of trim" amber warning light illuminated during an ILS coupled approach.

The first officer, who was at the controls, disconnected the autopilot, trimmed the aircraft longitudinally to relieve the pressure on the control column, and continued the approach to make a normal landing. This incident was not recorded in the technical log.

At Frankfurt a flight plan for Gatwick with Stansted as the alternate and an expected flight time of 70 minutes was filed with Air Traffic Control (ATC). The estimated time of departure was 0030 hrs on 5 January.

The weather information available included the 2350 hrs report showing that the RVR at Gatwick was 100 metres in freezing fog and no improvement was expected before 0600 hrs the following morning. The visibility at Stansted was 2 km.

Captain Nowroz decided to take-off on schedule and obtain later weather reports in flight, having had enough extra fuel taken on board to enable him to return to Frankfurt if necessary.

The aircraft left Frankfurt at 0036 hrs and near Wulpen came under the control of London Airways at 0113 hrs.

London Airways verified the RVR at Gatwick as 100 metres, and Captain Nowroz confirmed his intention to try to land at Gatwick. The controller gave a routine onward clearance, adding that Runway 27 was in use at Gatwick and repeating that the RVR was 100 metres. At 0123 hrs the controller reported that he had checked with Gatwick and the runway visual range was still 100 metres and there was no sign of improvement. Captain Nowroz replied that he would try to land at Gatwick, but as a precaution he obtained clearance to divert to Heathrow.

The aircraft called Gatwick Approach at 0127 hrs, reporting flight level 50 and giving an estimated time of arrival (ETA) at Mayfield, the non-directional beacon for the Gatwick control zone, of 0130 hrs. The controller responded with the landing conditions which included the RVR of 100 metres. He also asked if the commander intended to make an approach and received an affirmative reply. The aircraft was then cleared to 2,000 feet on the sea level altimeter setting (QNH) and at 0128 hrs directed it to turn on to a heading of 360° M to intercept the ILS localiser beam.

At this point the crew of the aircraft began their approach checks. The pressure altimeters were set to QNH and crosschecked: the Operator's weather minima applicable to Gatwick of 200 feet critical height (critical height means the minimum height above the elevation of the airfield to which an approach to landing can safely be continued without visual reference to the ground) and 0.5 mile RVR were checked, and the cursors on the radio altimeters were set to 200 feet on the port side and to 500 feet on the starboard. The compass heading cursor was set to 270°M in preparation for a go-around (missed approach). At 0129 hrs the commander told ATC that in the event of a go-around he would proceed to Mayfield and then to London (Heathrow). ATC gave the aircraft a heading of 300°M to close with the ILS localiser and then distances from touchdown of 13 miles and 11 miles. During the turn on to this heading the commander, who was at the controls, coupled the automatic pilot to the ILS, selected the "Glide-slope auto" mode on the flight director and the autopilot selector boxes, and switched on both altitude holds to hold 2,000 feet. The co-pilot's flight director was left switched off, so that only the basic ILS indications appeared on his instrument during the approach. According to the flight recorder trace and the cockpit voice recorder the flaps were then lowered in stages to 2°, 5° and 15° at speeds 223 knots, 200 knots and 166 knots respectively.

At 0131 hrs about 8 miles from touchdown the commander informed ATC that the aircraft was established on the ILS localiser. He received clearance to continue the approach and was given the airfield level altimeter setting (QEE). The surveillance radar at Gatwick showed that the aircraft was following the approach centre-line exactly. ATC advised the aircraft to climb on the runway heading to 2,000 feet (QNH) in the event of a go-around and then cleared it to land adding- that the wind was calm and the RVR was still 100 metres.

Approximately 39 seconds later the crew saw from the glide-slope pointers on their flight instruments that they were nearing the glide-slope. Shortly afterwards, when the airspeed was about 177 knots, the undercarriage was lowered and speed and height slowly decreased. At this point the commander asked the flight engineer to warn him if the "stabilizer out of trim" warning light illuminated as it had done at Frankfurt. The appropriate reference speeds of 114 knots (minimum approach speed) and 124 knots (go-around speed) were set on the adjustable reference "bugs" of the port and starboard airspeed indicators respectively. About this time the co-pilot drew the commander's attention to a single red light on the ground, the only one the crew saw during the approach, which the commander recognised as a light at the other end of the runway which was in fact a hazard light on Russ Hill. Some seconds after 0132 hrs when the landing gear was locked down the aircraft intercepted the glide-slope. The nose went down and the altitude hold switches clicked off. The airspeed according to the flight recorder was 150 knots. From the commander's recollection 25° flaps had been selected by this time but calculations indicate that they were still at 15°. The airspeed then began to build up and shortly after the aircraft had settled on the glide-slope the "stabilizer out of trim" warning light illuminated. The engineer warned the commander who then saw that the autopilot was trimming the aircraft nose-down. Thinking this was wrong he disconnected the autopilot by means of the control column button switch. This switch automatically sets the flight director to the "go-around" mode. To continue the approach with the flight director the commander would have had to re-select the "glide-slope manual" mode. This he said he did. At this time neither pilot noted the pitch indication on the flight director but the commander re-trimmed the aircraft slightly nose-up, using the control column trim switch. According to the co-pilot's recollection the commander then selected 25° flap, but energy calculations based on the flight recorder trace indicated that there had been no change of flap setting at this point.

The aircraft crossed the ILS outer marker on the glide slope at 0133 hrs and the commander called for 30° flap, which the co-pilot set. Calculations show that the change in the flight path at this point was compatible with a change in flap setting from 15° to 30°. The speed, according to the flight recorder, was 167 knots and the rate of descent about 1,000 feet per minute, although the pilots thought the speed was 140 to 145 knots, and the rate of descent about 600-700 feet per minute. As the flaps extended the rate of descent increased and the aircraft began to go below the glide-slope although it remained accurately on the localiser beam. The pilots remained unaware of the deviation from the glide-slope for some time; their recollection was that all the indications continued to appear normal.

The co-pilot had been briefed to call 500 feet on the radio altimeters and 700 feet on the pressure altimeters and this he said he did. The 500 feet call could not be identified on the cockpit voice recorder, but there was a call at 400 feet. The co-pilot thought that at this time the rate of descent was 1,000 to 1,200 feet per minute and the speed about 140 knots. These figures agreed reasonably well with those derived from the flight recorder. The commander queried the height of 400 feet and when it was confirmed he tried to trim the aircraft nose-up using the trim switch on the control column. There seemed to be no response; the aircraft appeared to pitch nose-down and felt nose heavy. Both pilots pulled back on the control column and at the same time the commander applied full power. Both pilots subsequently stated the control column could only be moved back about an inch.

The aircraft continued to descend and seconds later, as the nose began to rise in response to the application of elevator and power, it brushed through tree tops, knocked a chimney pot off a house, and then collided with tree trunks. This impact removed part of the starboard wing and the aircraft began to roll to the right. The aircraft broke clear of the trees and the starboard main wheels touched the ground in a field. The aircraft became airborne again, still rolling to the right, in a nose high attitude. Then the aft end of the fuselage collided with a house, which it demolished, and the aircraft disintegrated. The rear portion of the fuselage containing No 2 engine remained in the ruins of the house while the rest of the aircraft structure including Nos 1 and 3 engines spread itself over a wreckage trail of some 1,395 feet long. Fire broke out and fed by fuel spray from the ruptured tanks, destroyed the wings and fuselage and consumed most of the instruments, radios and controls on the flight deck.

The controllers at Gatwick who had been watching the progress of the aircraft on their radar screens, saw the blip disappear when indicating two miles from touchdown. At the same time the tower controller heard a double bang and, suspecting that the aircraft had crashed, telephoned the approach controller asking if the aircraft was still in radio contact. When he heard that it was not, he alerted the crash services.


1.2 Injuries to persons

Injuries Crew Passengers Others
       
Fatal 5 43 2
Non-fatal 3 11 1
None - -  

1.3 Damage to aircraft

Destroyed.

1.4 Other damage

One house destroyed and two houses damaged.

1.5 Crew information

1.5.1

Cormander Captain Rahim Nowroz, aged 37, held a valid Afghan Airline Transport Pilot's Licence endorsed for DC.3, DC.6, Convair 440 and Boeing 727 aircraft. These licences depended for validation on a six-monthly medical examination; Captain Nowroz passed his most recent examination on 27 October 1968. His last preliminary check was carried out on 1 August 1968 and his last route check on 19 May 1968.

He had accumulated a total of approximately 10,400 hours flying of which 512 hours were in command of Boeing 727 aircraft, and had made 16 flights into Gatwick in Boeing 727 aircraft, twice with First Officer Attayee as co-pilot. In the 28 days before the accident he had flown some 64 hours; during the last 7 days, 26 hours; and during the last 24 hour period, 5 hours. Before the flight on which the accident occurred he had been off duty for 21 hours.

Captain Nowroz learned to fly in England in 1956 and joined Ariana Afghan Airlines in 1957 as a co-pilot. He was promoted to a DC.3 captain in January 1960, and subsequently became captain on DC.4, DC.6, Convair and Boeing 727.

His Boeing 727 training began at the Civil Aviation Safety Centre, Beirut in January 1968. This 4 week course included conversion to jet flying techniques and familiarisation with the Collins FD 108 flight system. Captain Nowroz's performance during training was assessed as satisfactory. In the Spring of 1968 Captain Nowroz continued 727 pilot training with the Boeing Aircraft Company, Seattle and after 25 hours flying completed a Federal Aviation Agency check in April 1968. While he was based in Kabul in May 1968 he did 38 hours training on route check flights and received a good report after each flight.

His training was concluded with a two day 727 simulator course at Brussels in August 1968. Captain Nowroz rapidly adjusted himself to flying the simulator, but his examiner noted that rather than ask his crew, he had a tendency to do routine duties on the flight deck himself at the expense of 'handling the controls'.

1.5.2

The co-pilot First Officer Abdul Zahir Attayee, aged 31, held an American FAA Commercial Pilot Certificate and an Afghan Commercial Pilot's licence for single and multiengined landplanes; his most recent medical examination was on 8 August 1968. His most recent proficiency check was passed in January 1968 and route check in May 1968.

He had accumulated a total of 3,259 hrs flying of which 210 were as co-pilot in Boeing 727 aircraft, and had flown 8 times into Gatwick, thrice in DC.6 aircraft and 5 times in Boeing 727 aircraft. In the 28 days before the accident he had flown 26 hrs 10 minutes; during the last 7 days, 5 hours; and during the last 24-hour period, 5 hours. Before the flight on which the accident occurred he had been off duty for 21 hours.

First Officer Attayee joined Ariana Afghan Airlines as a student pilot in 1960. He received pilot training at Parks Air College, USA in 1961 and was issued with an FAA and an Afghan Commercial Pilot's Licence in May 1962 and in December 1962 respectively. On a periodic training flight in June 1963 he was assessed as 'average - shows promise'. His Boeing 727 training began in the winter of 1967 at the Civil Aviation Safety Centre, Beirut, where he completed procedure training and 12 hours in the flight simulator. His assessment was 'steady, slow improvement'. After 6 days training on the 727 with the Boeing Aircraft Company, Seattle, in January 1968 he completed just over 10 hours flying. It was remarked during this course that First Officer 'Attayee was 'weak on instrument cross checks, forgets check list'. Subsequently in May 1968 after he had completed approximately 14 hours route training on the 727 in Kabul he was reported as a 'good first officer'.

In September 1968 he underwent two days training and a mock proficiency check on a 727 simulator at Brussels (his mandatory proficiency check was not due until 24 January 1969). The supervisor remarked 'period incomplete, recommend additional training prior to continuance of check'.

1.5.3

The Flight Engineer Flight Engineer Mohammed Hussain Furmuly, aged 30, a ground engineer who qualified as a flight engineer in June 1968, attended a three months Boeing 727 flight engineer's course at the Pan American Airlines school at Miami, which he completed in November 1968. In the same month he passed the Federal Aviation Agency flight engineer's flight check and was issued with a temporary airman's certificate dated 2 November 1968 and later with a permanent airman's certificate for the same date. He also held a valid Afghan licence.
He completed the route checks from Kabul on 24 December 1968.

Before the flight on which the accident occurred Flight Engineer Furmuly had been off duty for 21 hours.

1.6 Aircraft information

The Boeing 727 is a medium range low-wing transport aircraft powered by three turbofan engines, one mounted each side of the rear fuselage and the other centrally at the base of the fin assembly. The power operated variable incidence stabilizer (tailplane) and elevators are mounted near the top of the fin.

YA-FAR was built by the Boeing Aircraft Company Limited, Renton, Washington, USA in 1968-and was issued with a United States of America certificate of airworthiness for export on 25 March 1968. It was purchased by Ariana Afghan Airlines and registered in Afghanistan on 29 April 1968. The Afghan Air Authority issued a certificate of airworthiness in the "Commercial" and "Air Carrier" categories on 14 May 1968. This certificate of airworthiness was valid at the time of the accident, the aircraft having been maintained under an approved continuous maintenance system. The aircraft had completed a total of 1,715 hours flying.

At take-off from Frankfurt the weight of the aircraft was 60,895 kg. This weight included 1,362 kg of extra fuel which was uplifted as a bad weather reserve and had not been recorded on the load sheet. The centre of gravity (CG) was at 25.6% mean aerodynamic chord (MAC). The calculated weight at the time of the accident was 56,259 kg and the calculated CG was at 25.71 MAC. These weights and CG positions were within the authorised limits.

Fuel of specification PWA 522 was used and calculations show some 9,000 kg would have been in the tanks at the time of the accident.

The primary trim device in the pitching plane on this type of aircraft is the moveable stabilizer (tailplane). The primary control for manoeuvring in the pitching plane is the elevator. To dispose of the load on the control column produced by elevator deflection the incidence of the horizontal stabilizer is changed to take up the aerodynamic force and allow the elevator to return to neutral. Thus the elevator and control column are neutral and centralised except during the initiation of changes in pitch attitude or during compensation for changes of trim due to changes of aircraft configuration or flight regime.

When the autopilot pitch axis is engaged it manoeuvres the aeroplane or compensates for changes in flight regime or configuration by first deflecting the elevator and then automatically trimming the aeroplane by changing the stabilizer incidence. An elevator position sensor provides a feed-back signal to the auto-trim system and the stabilizer incidence is changed by the slow-speed 'cruise trim drive' motor whenever the autopilot pitch commands cause the elevator to exceed a certain deflection. Where pitch or trim changes occur rapidly or in combination, elevator deflection may be demanded faster than the stabilizer incidence can be changed. If when this happens the stabilizer becomes out of trim relative to the elevator for longer than the time delay incorporated in the circuit, an amber 'stabilizer out of trim* warning light illuminates on the flight deck. It alerts the pilot to the possibility of an untrimmed load on the control column if he were to disengage the autopilot while the light was on.

 

1.7 Meteorological information

On the night 4-5 January the south of England lay in a relatively moist air stream. There had been thick fog during the day and it had been expected to clear as the wind strengthened ahead of a depression that was moving slowly south-east. This clearance was not complete and there was patchy fog in the Gatwick area. By 2300 hrs on 4 January there were clear skies at Horsham, at Crawley Radio Sonde station (7 miles south of Gatwick) and over the North Downs. The moon was visible all night through the fog at Gatwick. The top of the fog is unlikely to have been more than 250 feet above the surface of the airport.
Before departure the co-pilot reported to the despatch office at Frankfurt and was informed verbally of the route weather and the situation at Gatwick. He was also given a copy of the forecast issued for Gatwick for the period 2300 hrs on 4 January to 0700 hrs on 5 January:

Surface wind Variable 2 knots
Visibility 100 metres
Weather Fog
Cloud Sky obscured

gradually becoming between 0300 and 0600 hrs:


Surface wind 210 degrees 5 knots
Visibility 500 metres
Weather Fog
Cloud 8/8 stratus at 200 feet

and the 'actual' weather report for Gatwick at 2350 hrs on 4 January:



Wind Calm
Visibility 100 metres
Weather Freezing fog
Cloud Sky obscured
Temperature Minus 2° C
Dew point Minus 3° C
Barometric pressure 1018 millibars
No significant change  

After it left Frankfurt the following actual weather reports for Gatwick were passed to the aircraft:

Gatwick 0020 hrs 5 January the same as Gatwick 2350 hrs 4 January;

Gatwick 0118 hrs 5 January:

Wind Calm
Visibility 50 metres
Weather Freezing fog
Cloud Sky obscured
Sea level barometric pressure (QNH) 1018 millibars
Aerodrome barometric pressure (QFE) 1010 millibars
Temperature Minus 03°C
Runway visual range 100 metres

The broadcast weather report for Heathrow Airport, London at 0115 hrs was:


Wind 190 degrees 5 knots
Visibility 2,500 metres
Cloud Sky clear
   

Stansted Airport was listed on the flight plan as the alternate and the crew took on enough fuel to return to Frankfurt if necessary. At both these airfields the weather was suitable for landing throughout the night.


Ariana (Afghan) Airlines weather minima for Gatwick ILS were as listed in Jeppesen - half a statute mile RVR and 200 feet critical height.

1.8 Aids to navigation

The aircraft was equipped with a full instrument panel including Collins FD-108 integrated flight system, VOR and ILS and was cleared for operation down to weather minima of 200 feet critical height and 0.5 mile runway visual range. All the equipment was serviceable.

1.9 Communications

Two-way R/T communication between the aircraft and air traffic control was satisfactory and routine; a transcript of Gatwick approach control voice recording on frequency 119.6 MC/S is at Appendix I.
The cockpit voice recording was weak and indistinct but with the assistance of the crew and the approach control frequency recording the transcript at Appendix II was produced.

1.10 Aerodrome and ground facilities

Gatwick airport, elevation 194 feet, has a single concrete runway orientated 09/27 2,499 metres long and 46 metres wide. At the time of the accident its lighting, including the touchdown markers for runway 27, was at 100% high intensity and the visual approach slope indicator system (VASIS) at 80%. The approach lighting for the runway, consisting of a centre line of high intensity white lights with 5 bars was at 30%, The airport facilities including locator beacon GE, surveillance radar and distance from touchdown indicator were all serviceable. About two hours after the accident, at 0315 hrs the ILS ground equipment was subjected to a post-accident ground check and was found to be satisfactory. At 0640 hrs a post-accident flight check showed that the transmissions were well within the permitted tolerances.

Since only surveillance radar was available to monitor the approach no glide-slope information could be given to the aircraft.

1.11 Flight recorder

The main unit was installed in a pressurised container located in the rear fuselage near the aft stairs. It recorded, by means of scriber engravings on a steel foil tape, pressure altitude, indicated airspeed, magnetic heading, and normal acceleraticm to a common time base. Graphs derived from the records are at Appendix III.

1.12 Wreckage

Inspection at the scene of the accident showed that the aircraft had flown through tree tops 60 feet above the ground, 1.5 miles from the threshold of runway 27. About 264 feet further on it had brushed off the chimney pots of a house some 40 feet above the ground before striking more trees that tore off the starboard wing tip and aileron and outer flap. Then the aircraft began to roll to the right and the starboard main wheel touched the ground for a short distance after which the aircraft became airborne again in a nose high attitude. Scorch marks on the ground show that the engines were developing high power at this stage. Then the aft end of the fuselage collided with a house, which it demolished, and the aircraft disintegrated. The rear part of the fuselage containing No 2 engine and with the empennage attached remained among the ruins of the house. The rest of the aircraft including Nos 1 and 3 engines, which became detached, was spread over a wreckage trail some 1,395 feet long. Fire broke out and was fed by fuel spray (aviation kerosene) from the ruptured tanks. The wings and fuselage including the flight deck were largely consumed by the fire.
It was established that at the time of the accident:

i. Landing gear was down

ii. Flaps were extended to 30°

iii. Leading edge slats were extended

iv. Horizontal stabilizer was set to 4.25 units nose up trim

v. Elevator was fully up

The flight deck was gutted by fire and all instruments, including the flight director system, were either melted or reduced to ashes. It was possible to establish only that the barometric setting of the automatic pressurisation controller at the flight engineer's station was 1013 mbs the standard flight level setting.
The wreckage was removed to a hangar for a detailed examination that revealed that at the time of impact all three engines were under power and at high rpm. There was no indication of pre-crash mechanical failure in the engines and no evidence of pre-crash defect or failure of the ailerons, rudder, elevators or horizontal stabilizer. All hinges, brackets and hydraulic jacks were in good condition.

1.13 Fire

Fire had occurred on the ground after impact when the fuel tanks and fuel system were ruptured. Damage by fire was particularly severe in the flight deck area.
The fire brigade was informed at 0138 hrs and despite difficulties due to fog and the need for a diversion via a bridge to cross a main railway line the first appliance was on the scene at 0156 hrs. Ten appliances with pumps and ten miscellaneous fire vehicles from the Surrey, Sussex and the airport fire brigades attended.

1.14 Survival aspects

During the break-up of the structure after the collision with the house some passengers and their seats were thrown out. The crew said that they escaped from the wrecked flight deck through the window escape exits. The flight engineer injured his ankle on dropping to the ground and was obliged to hobble away from the wreckage, while the commander and the first officer assisted a number of passengers from the burning wreckage.

One passenger went back to rescue members of his family, and beat out the flames on the clothing of another passenger who had been thrown clear.
Residents in nearby houses and several police officers reached the scene a few minutes after the accident. In spite of the flames and a number of explosions they worked with commendable courage to rescue a number of survivors before being driven back by the heat.

Of the 62 persons on board the aircraft, 14 survived; 7 died from injuries sustained in the accident, and 41 died as a result of asphyxia or burns. Of the three persons in the house, two were killed and one (a baby) survived.

1.15 Tests and research

The elevator artificial feel system and the power control units were examined for the Accidents Investigation Branch by their respective manufacturers under the supervision of the United States National Transportation Safety Board. In each case the components were found to function satisfactorily. No defect that could have caused a failure of the power control units was found, and no binding or erratic performance was noted during any of the tests. No defect came to light that could have caused or contributed to the accident.
The manually operated electric trim actuator and the auto-trim actuator were checked and rig-tested in the BOAC workshops under the supervision of an AIB Investigator. All functioning checks and inspections showed the units to be in a satisfactory state, from which it was concluded that the stabilizer trim, the auto-pilot and cruise trim systems were operating normally at the time of the accident.

From flight tests on a Boeing 727 aircraft and the simulator a flight recorder trace was reproduced for comparison with the flight recorder traces of the accident flight. Observations were made during the tests of the aircraft attitudes, rates of descent and responses to control column movement and loads. Recordings were made of sounds associated with the operation of flight deck equipment in an attempt to identify similar noises on the cockpit voice recorder in YA-FAR. The attempt was only partially successful. Mechanical movements such as the operation of the stabilizer trim actuator were easily identified but operations involving electrical switching; eg flight director mode selection could not be identified.
Calculations were made from the flight path derived from the flight recorder data to determine the power settings, rates of descent, and body angles at various stages of the approach. These are noted at Appendix 4; they were compatible with observations made during the flight tests.

When the commander initiated recovery action the aircraft was descending at about 150 knots and 1,500 to 2,000 feet per minute. At this speed - more than 30 knots above the reference speed - it is theoretically possible for a properly executed pull-up manoeuvre to be accomplished with a height loss of as little as 55 feet. In tests on a simulator this ideal was not met and as much as 300 feet was taken to recover although this figure was reduced to 100 feet as the pilot repeated the exercise.

1.16 Precision approach radar

Precision Approach Radar (PAR) was permanently withdrawn from-operational service at Gatwick airport on 8 February 1968. Before that date PAR would monitor aircraft carrying
out ILS approaches whenever the cloud was 300 feet or less or the RVR was 1,100 metres or less. The RVR at the time of the accident was 100 metres and if the facility had been in use YA-FAR's approach to Runway 27 would have been monitored. The precision radar controller is required to warn the pilot when the aircraft goes outside the safe approach funnel and particularly if it descends below the glide-slope. The safe approach funnel is defined as 'a funnel subtending approximately 0.5 degrees above and below the glide-slope and approximately 2 degrees either side of the final approach track'. If an aircraft remains in the funnel a successful visual landing may be reasonably expected. If an aircraft drifts laterally out of the funnel or its movement from the glide -slope centre line indicates that it will shortly go below the funnel the controller would immediately inform the pilot. If the pilot did not subsequently adjust his rate of descent and the aircraft continued to descend below the glide-slope the precision controller would advise the aircraft to maintain its present height or to climb, according to circumstances.
On the approach that ended in the accident, YA-FAR kept well within the safe approach funnel and on the glide-slope until it had descended to a height of about 1,000 feet approximately 3.75 miles from touchdown. Then the rate of descent increased. If the approach had been PAR-monitored the controller would have been alerted at this time to the possibility that the aircraft would shortly go below the funnel and he would have advised the pilot of his deviation from the glide slope and then, if he did not adjust his rate of descent, to maintain height or climb.

 

2. Analysis and Conclusions

2.1 Analysis

In the sequence of events leading to this accident there are three stages:

a. the departure from Frankfurt and flight to the London area;

b. the decision to make an approach to land at Gatwick with a Runway Visual Range of 100 metres;

c. the conduct of the initial and final approaches to Gatwick.


Flight from Frankfurt to the London area

There was no reason why the commander should decide not to fly to the London area. The weather information available supported his decision. Although the Gatwick weather was bad, Heathrow Airport, London, was suitable for landing and Stansted was available as an alternate, and as a further precaution he had taken on board enough fuel for a return to Frankfurt, where the weather would remain favourable.

The decision to approach for a landing at Gatwick with RVR 100 metres

Commanders of British registered aircraft were prohibited by legislation in force at the time of the accident from commencing or continuing an approach to an airfield that reported RVR less than their declared minima, which in every case were considerably greater than 100 metres. This legislation did not extend to foreign registered aircraft operating over the United Kingdom. Afghan legislation and Ariana (Afghan) Airlines instructions prohibited landing when the RVR was less than the declared minima (in this case half a statute mile) but allowed aircraft commanders discretion in deciding whether or not to continue their approach down to critical height (in this case 200 feet). The question of an approach to Gatwick down to his critical height was therefore a matter for Captain Nowroz's own judgement of the weather and his opinion of the chances of a successful landing thereafter.

When he sighted the English coast he could see that the fog was patchy and decided that since patchy fog shifts quickly he would make an approach with a view to landing at Gatwick. About 15 minutes before his estimated time of arrival at the airport he confirmed visually that the fog was in patches. He could see lights on nearby roads, and the lights of London were visible. He again considered the question of an approach to Gatwick and came to the conclusion that it would be worthwhile. That his visual observation of the weather conditions weighed most heavily in arriving at this conclusion may have led to too much concentration on a search for reference outside the flight deck during the final stages of the fatal approach.
Experience in the United Kingdom has shown that surface fog on an otherwise clear night can lead the most careful pilots into disastrous errors of judgment when anticipated visual references fail to appear or when references in use become suddenly distorted or disappear. It was this experience that led to the legislation referred to above, and to its extension in September 1969 to include foreign registered aircraft operating over the United Kingdom.

The difficulties involved in landing in conditions of ground fog were well known at the time of the accident, although the commander of YA-FAR may not have been fully aware of the deceptive and misleading nature of such conditions. His reliance on visual observation from a vantage point in clear air and good visibility at altitude appear to have led him to err in his judgment and decide on an approach in the face of repeated reports from the airport of the conditions existing at the point of touchdown. However, there should be no undue risk in an approach down to 200 feet followed by a properly conducted go-around or overshoot. The commander's decision to make the approach was not in itself a cause of the accident.

Conduct of the initial and final approach to Gatwick

i. Initial approach (from 15 to 6 miles)

A reconstruction of the profile of the approach from about 15 miles out can be seen in the diagram at Appendix 4. This diagram has been compiled from the evidence of the crew, the flight data recorder traces (Appendix 3), the cockpit voice recorder transcript (Appendix 2), and the transcript of the R/T communications (Appendix I). A study of this reconstruction together with associated tracking information reveals that from about 15 miles at 2,000 feet the height and closure on to the ILS centreline were in accordance with the Ariana procedures until the aircraft reached about 6 miles at 1,800 feet, but that during the next section of the approach there were a number of departures from these procedures with respect to speed, flap selections and power settings. With decreasing speed the flap setting programme should be:

At 200 knots select 2° flap
At 180 knots select 5° flap
At 160 knots select 15° flap
At 150 knots select 20° flap
At 140 knots select 30° or 40° flap.

Thereafter the speed should be adjusted to threshold speed plus 10 knots plus half the wind factor (on the occasion of the accident there was no wind factor). On the approach that terminated in the accident

2° flap was selected at 223 knots
5° flap was selected at 200 knots
15° flap was selected at 166 knots

These speeds were within the operating limits for the aircraft. After 15° flap had been selected the speed decreased to 143 knots and then increased to 176 knots by the time the landing gear had been selected down. Since at this stage the aircraft was being flown by the autopilot this inaccuracy in the speed reflects inaccuracy in handling the power.

(ii) Final approach (from 6 miles)

As can be seen from Appendix 4 the aircraft approached the glide-slope at 6 miles with 15° flap and undercarriage down. The undercarriage had been selected down at the recommended position (ie 1.5 dots 'fly up' on the ILS indicator) but at an airspeed that was considerably higher than that recommended. The next two items in the recommended sequence (25° flap at 1 dot 'fly up' and 40° flap at glide-slope interception) do not appear at the appropriate times on the cockpit voice recorder and energy calculations confirm that they were omitted. The autopilot had to demand a larger than usual nose-down pitch to set the aircraft on the glide-slope, and as a result the airspeed began to increase because the aircraft was by then descending with less than the recomnended flap, and therefore less than the anticipated drag. The increasing speed produced more lift and the autopilot had to demand more nose-down trim to keep the aircraft on the glide-slope. The application of nose-down elevator by the autopilot eventually outstripped the system's ability to trim out the load on the stabilizer, and this resulted in the illumination of the "stabilizer out-of-trim" warning light while the trim wheel was winding forward. To pilots unaware that the flaps had not been set appropriately for the descent this combination could appear to be incorrect and the assumption wuld follow that something had gone wrong with either the autopilot or the trim mechanism.

The commander was already aware that the out-of-trim warning light had a habit of illuminating in circumstances not clearly understood, so he disconnected the autopilot and then according to his statement he reset the flight director to "glide-slope manual".

Calculations based on the rate of descent and speed shown on the flight recorder trace indicate that at 1,550 feet (Point C, Appendix 4) the power had been reduced to 20% take-off thrust (approximately flight idle). At about 1,250 feet, five seconds after passing the outer marker 30° flap was selected. The cockpit voice recorder and relevant energy calculations show that the flaps moved from 15° to 30° without the intermediate 25° having been selected first. This uninterrupted fifteen degree increase in flap angle resulted in a marked nose-down pitch as the flaps extended and a marked increase in the rate of descent and a reduction in airspeed that was not offset by increasing the power. The aircraft immediately began to go below the glide -slope, leaving it at a height of 1,200 feet and at a rate of descent that stabilized at about 1,200-1,400 feet per minute, which is about twice the rate appropriate to a descent on a 3 glide-slope in the prevailing conditions.

The pilots do not appear to have noticed this deviation from a normal approach for some time and no attempt to correct it appears to have been made for about 45 seconds. Point F (Appendix 4) marks the first substantial increase in power derivable from calculations. Both pilots, when questioned further about this section of the flight, said that during this time all the indications appeared normal to them. Although it was not possible to establish from the wreckage whether or not the flight director was working properly, there is no evidence to suggest that it was not.

If it was working properly it would during this period have been giving strong fly up commands provided it had been correctly set to the glide-slope manual mode. If it had been inadvertently selected to G/S auto mode the computer of the integrated flight system would not have provided glide-slope tracking information to the V-bars until the aircraft intercepted the glide-slope again. If it had been inadvertently selected to VOR/LOC mode, the computer would not provide glide-slope tracking information to the V-bars at any time. The annunciator lights would have indicated what mode the flight director was in but if this indication had been missed the commander may not have been aware that the V-bars were not presenting glide-slope tracking commands. They would have commanded whatever pitch attitude had last been selected on the pitch trim command control knob.

Analysis of YA-FAR's flight path showed that the pitch attitude of the aircraft was between 4° and 7° nose-down in the final stage of the approach, so that if the control knob selection had been about 5° nose-down (the maximum) the V-bars would have been neutral, that is, giving the same indication as they would have done with the aircraft on the glide-slope and the flight director in the appropriate glide-slope mode.
It was not possible to establish from the wreckage and flight tests what mode selection had been made, but according to the pilots' statements the flight director was last used on the climb from Frankfurt, when the pitch control would have been set to 5 or 10 nose-up. In this case with either VOR/LOC or G/S AUTO selected during the final stage of the approach the V-bars would have given a 10 to 15 pitch up command. The raw ILS glide-slope pointer would also have been indicating fly up and the vertical speed indicator would have been showing too high a value for a normal descent on the glide-slope.

It is difficult in these circumstances to explain why there was no communication on the record between the pilots during this period. The inference is that they were both directing their attention outside the aircraft, searching for the aerodrome lights or some other visual cue to help them conduct the approach, rather than to the flight instruments. The crew's evidence was that they saw only one light during the approach. This was established as the hazard light on Russ Hill, although the commander placed it 'at the other end of the runway'. This light was specially observed during a night ILS approach to Gatwick in a Boeing 727 in conditions where other visual references on the ground were obscured. The light appeared to be higher and nearer to the aircraft than it actually was, creating the illusion that the normal approach path was too high. It is possible that by a similar process on the night of the accident the appearance of the light prevented the commander from detecting that his approach was too low.

If PAR had been in use, warning from the controller would have been given to the pilot during the first half of this period, ie about 26 seconds after the start of the high rate of descent mentioned above. Thus the pilot would have received this advice by the time the aircraft reached about 600 feet above the ground leaving some 25 seconds for recovery to be made before the aircraft reached the ground. In this particular case therefore had the approach been monitored by PAR the pilot would have been warned in time to avoid the accident if he took action promptly.

During the period of about 45 seconds when the aircraft was descending on the glide-slope without comment from either pilot the aircraft was slightly out-of-trim nose-down, and became more out-of-trim as the speed decreased from 167 to 148 knots. The profile (Appendix 4) suggests that the pilot was compensating for this to some extent by applying a certain amount of up elevator, probably quite automatically. There is no evidence from the cockpit voice recorder of re-trimming at this stage. When the co-pilot called 400 feet the aircraft was about 300 feet from the ground. It took some six seconds for the commander to absorb and respond to this information during which time the aircraft descended a further 120 feet. At this point the pilots thought that the aircraft pitched nose-down, but the only nose-down pitch of any magnitude recorded on the flight recorder trace was when the flaps were selected to 30° some 45 seconds earlier. They also reported a restriction in the movement of the control column but it was established that when the impact occurred from evidence in the wreckage the elevator was fully up.

The commander's response to the situation - to apply full up elevator and full power was correct, but too late. As many as eight seconds could have been required for the engines to spin up to full power, and since the application of elevator and power came when the aircraft was about 150 feet from the ground, still descending, there was not enough height for complete recovery to be made.

It is perhaps worth comment that it was noted during training that the commander has "a tendency to do routine flight deck duties himself at the expense of handling the controls" and that the co-pilot was "weak on instrument cross checks and forgets the check list". These are errors commonly noted when pilots convert from piston to more complicated jet aircraft. Doubtless they were attended to by the time the training was complete but if they were to re-appear at a time of stress or anxiety they could lead to an insufficiently high standard of flight deck management for operations in this type of aircraft.

2.2 Conclusions

(a) Findings

(1) The documentation of the aircraft was in order, except that 1,362 kg of fuel up-lifted as reserve was not included in the load sheet.

(2) The weight and trim of the aircraft were within the appropriate authorised limits for take-off and landing.

(3) No evidence of malfunction of the aircraft, its systems or the radio navigational aids available came to light during the investigation.

(4) The flight from Frankfurt to the London area was in order, and routine.

(5) The deceptive nature of the weather conditions led the commander to an error of judgment in deciding to make an approach to Gatwick.

(6) The commander's decision to conduct an approach was not in itself a cause of the accident.

(7) Incorrect flap configuration at glide-slope interception led to a temporary out-of-trim condition during the automatic approach and the illumination of the stabilizer "out-of-trim" warning light.

(8) The commander interpreted the "out-of-trim" warning light as indicating a possible malfunction and disconnected the auto-pilot.

(9) Out-of-sequence and late selection of 30° flaps from 15° while the-aircraft was being flown manually resulted in an increase in the rate of descent, causing the aircraft to go rapidly below the glide-slope.

(10) The commander did not become aware of the deviation from the glide-slope until it was too late to effect a full recovery.

(11) The pilot's attention was probably directed outside the aircraft at the critical time in an attempt to discover sufficient visual reference to continue the approach rather than to the flight instruments.

(12) Monitoring by precision approach radar would have warned the pilots of the deviation in time, if corrective action was taken promptly, to avoid the accident.

(b) Cause

The accident was the result of the commander inadvertently allowing the aircraft to descend below the glide slope during the final stage of an approach to land until it was too low for recovery to be effected.

 

3. Compliance with Regulations

In conducting this investigation the provisions of Regulation 7(5) of the Civil Aviation (Investigation of Accidents) Regulations, 1951 have been complied with. Captain Nowroz was offered the opportunity of exercising the rights conferred by the regulation and he was informed of the facilities available for that purpose. He made representations in person and these have been taken into account in preparing the report. It was not found necessary to alter the opinion as to the cause of the accident.

G M KELLY Inspector of Accidents
Accidents Investigation Branch Board of Trade
June 1970

Appendix 1 Part A

Civil Aviation Department
Board of Trade

Reason for extract Accident Aircraft, Ariana 701 (YA-FAR) (Ariana Afghan Airline Co. Ltd.)
   
Ground station London Air Traffic Control Centre
   
Callsign London Airways/Radar
   
Extract Ref. No. 1
   
Frequency 127.1 MHz
   
Facility Airways
   
Type of log Radiotelephony recording
   
Period covered by extract From 0108 GMT on 5 January 1969
  To 0140 GMT on 5 January 1969

Notes:

1. Time signals may be injected into the recorder by the following methods:

(a) Orally by Board of Trade personnel.
(b) Automatically by a time injection unit in the form of three letter morse signals.

These signals may or may not occur simultaneously with speech, but for clarity the three letters are bracketed together and entered either in their correct position or immediately after the word in which the time signal occurred.

2. All time signals appearing in Column 4 are entered in Column 5, including the decode of the automatically injected signals to assist in the interpretation of the log.

3. The entries in Columns 2 and 3 have also been made to assist in the interpretation of the log and they do not necessarily occur on the recording, either in the form given or in any other form. Where they do not appear in the form given or in any form in Column. 4, the entries in Columns 2 and 3 represent the opinion of the transcriber and are based on his knowledge of the recording.

4. All significant pauses in a message are indicated by a space of about half an inch. Where possible the duration of the pause is given in the "Remarks" column.

5. Words which are doubtful are indicated in Column 4 by a series of question marks at the appropriate place. When possible the duration or number of such words and/or a probable interpretation of them is given in the "Remarks" column.

6. Words which are unintelligible are indicated in Column 4 by a series of question marks at the appropriate place. In addition, the word "Unintelligible" and if possible the number or duration of the missing words are entered in the "Remarks" column.

F. A. ABBOTT
Officer i/c, Transcription Unit,
Southern Divisional Office, Heston.

7 January 1969