On the night of February 21, 1969 the Qantas Boeing 707-338C VH-EAB was subjected to aerodynamic loads that thoughorly tested its structural strength. The aircraft was operating the Singapore - Bangkok - Bahrain sector of the scheduled Sydney (Kingsford Smith) - London (Heathrow) service as flight QF739.

The crew who had just taken over the aircraft at Singapore, had flown into this port the day before, flying the Sydney - Perth - Singapore leg. On signing for the aircraft, the crew were advised that for all practical purposes it was fully serviceable. However there had been a history in the aircraft's Technical Log of comparison warnings between the artificial horizons for the Captain and First Officers' instruments.

If the two instruments differ by more than five degrees a 'clacker' alerts the crew aurally that all is not right, and a 'red light' flashes on the instrument panel, providing a back-up 'visual' alert. The procedure was then to check the 'standby' artificial horizon instrument, located on the centre instrument panel, to determine which instrument was providing the false indication. If there is a fault or a power failure to a flight instrument, said fault is normally accompanied by a 'flag' which partially covers the faulty instrument.

Unbeknown to the flight crew, an electrical fault, buried deep in the bowels of the under-floor electronics bay, would shortly cause havoc on the flight-deck.

On the Singapore - Bahrain sector tha aircraft was lightly loaded with only 72 people on board - 62 passengers and 10 crew members. It was also approximately 20 tonnes under its maximum take-off weight. It was these facts that probably saved everyone from the events that were to shortly unfold. It was suggested by Boeing, on investigating the incident, that had the aircraft been significantly heavier then she would probably not have survived the stresses that were inflicted on the aircraft's structure.

The Flight Engineer inspected the Technical Log, noted the previous history of defects, and ensured that the aircraft was fully serviceable and that the maintenance engineers had signed to this effect. The pilots were not informed of any of these details, nor was there, at that time, any requirement for them to be informed. None of the pilots viewed the 'Technical Log' nor was there any requirement for them to do so.

The First Officer, who was undergoing flight-training, flew the Singapore - Bangkok sector. He also carried out the take-off from Bangkok, with the aircraft's take-off weight logged at 290,000 pounds (132,000 kg) which was well below the maximum of 336,000 pounds (152,700 kg).

The aircraft was stabilised in normal cruise mode, travelling at 35,000 feet with an I.A.S. of M 0.81. The autopilot was flying a radial away from Jiwani, a small town near the Pakistani border with Iran towards a waypoint out over the Arabian Gulf. There was no visual horizon.

With the passenger cabin now in darkness, the Flight and Cabin Crew had started rotating for their meal / rest breaks. The Captain was back on the flight deck, having finished his break while the First Officer was in the Crew Rest Area, just opposite the forward galley and about 20 feet (6 metres) behind the flight deck door.

The First Officer had been dozing when he felt the aircraft start to turn to the left. His initial reaction was that the PIC was turning to avoid some weather. The turn continued. The First Officer's then thought that the weather at Bahrain had deteriorated and that the Captain had elected to return to Karachi to upload more fuel.

The First Officer was then startled when the mach / airspeed warning bell started to ring. This bell is the warning that the aircraft is exceeding its legal maximum speed. It is factored to sound slightly before the aircraft will sustain structural damage of a serious or even fatal nature. And the bell kept ringing!

The First Officer's first reaction was to get back to the flight deck. Unfortunately at that point in time everyone on the aircraft was being subjected to an enormous 'G' force, which forced him to the cabin floor. Screams and cries of panic were coming from the passenger cabin. The Chief Steward and a Flight Hostess who had been sitting on the jump-seats nearby, were both on the floor, unable to stand up. It was later estimated that at that point in time the 'G' force being exerted on the aircraft was some 4.57. The First Officer crawled over them to reach the flight deck.

On entering the flight deck he managed to climb into the Second Officer's seat, which is located directly behind the Captain's seat. From this position it was possible for him to see where the problem lay and to give advice on what control inputs were needed to recify the 'loss-of-control' situation. At this point the aircraft began to porpoise quite violently. The captain's artificial horizon instrument wa stuck indicating a 30 degree bank to the right, while the standby and the co-pilot's artificial horizon instruments agreed with each other. There were no 'warning' flags on any of the instuments.

How did this loss-of-control develop in the first place? The Captain had glanced away from his main instruments to his right, to scan the centre pedestal. When he returned to look at his main instrument panel he saw that his HDI was indicating that the aircraft was in a 30 degree uncommanded bank to the right. Without cross checking the First Officer's instrument or the standby Horizon between the two pilots, the Captain corrected for this non existent bank. The aircraft immediately responded by rolling to the left robustly, became inverted and dived away towards the ground.
 
In the next 40 seconds the aircraft lost 19,000 feet of altitude. The Flight Data Recorder (FDR) would later disclose that the aircraft had attained a maximum speed of Mach 0.93 although the feeling was that it had been briefly supersonic, but compressibility issues around the pitot tubes had caused the Airspeed Indicators to under read the actual speed.
 
The Flight Data Recorder recorded a maximum positive 'G' figure of 4.57 while a significant negative 'G' figure of 0.63 was recorded. The flying training that the First Officer had already acquired allowed him to safely fly an aircraft using limited instruments. From his position behind the Captain, he was then able to give the Captain advise on how to regain effective control of the aircraft.

With the aide of the other serviceable instruments, control of the aircraft was regained. The descent had been arrested at 16,800 feet (7,600 metres) with some 40 seconds elapsing since the 'loss-of-control' commemved. With the recovery complete, four very shaken crew-members looked at each other!

The aircraft appeared to be undamaged, so after some discussion, the Captain decided to climb back to the assigned altitude of 35,000 feet (10,600 metres) and continue as planned to Bahrain where there were maintenance facilities, hotels and a Qantas base. Once re-established in a stable cruise, the Captain decided to go back into the passenger cabin the check on the condition of the passengers.

A young woman had been sitting right down the back of the aircraft with a very small baby on her lap. After the ‘high dive’ she contacted the cabin crew in a very distressed state, asking where her baby was. She didn’t look pregnant, and at first the crew thought she was hysterical. However, it did not take too long to convince them that she did indeed have a small baby in her arms at the time of the aircraft’s upset, and that it had now disappeared. As one can imagine, the state of the cabin was one of total chaos with debris everywhere. A search for the baby was started and some time later, under piles of cushions, trays and other associated debris, it was found next to the class divider. It had floated up out of its mother’s arms and forward along the full length of the economy cabin. When the negative ‘G’ force had come off, it had descended to the floor to be then covered up by the cabin trash. It had been fast asleep the whole time and was quite uninjured.

The First Officer returned to the co-pilot's seat, as the HDI on his side of the instrument panel was unaffected by the fault that had befallen that on the Captain's side. Before the Captain went back to inspect the cabin, he had instructed the Flight Engineer to set the thrust on the engines to maintain the original cruise speed. After a little while, the First Officer's nerves got the better of him, so he requested that the Flight Engieer reduce the cruise speed by some 25 knots, which would put less strain on the airframe, just in case some damaged had been sustained during the 'loss-of-contol' incident. When the Captain returned to the cockpit, the First Officer advised him of his actions, which were approved.

The uneventful landing at Bahrain was conducted by the Captain. Ambulances met the aircraft, but in fact, only one person was injured. A man, one of the few passengers who had their seat-belts only loosely fastened, found himself up on the roof during the porpoising. He said later that he thought he was in heaven as he could see all the other people down below!  When the negative ‘G’ came off the aircraft, he came down to earth very rapidly. He hit the top of his head on the corner of an ashtray on the seat armrest. His scalp wound required seventeen stitches. The passengers were later dispersed to Gulfair and British Airways to continue their journey.

Once all the passengers had been cared for, the writing of the reports commenced. The Captain was on the phone to Sydney, and Sydney had been on the phone to Boeing. The aircraft landed in Bahrain about 1 am local time but the crew were still up at 10 am. The aircraft had been grounded and the crew were all held 'out of service' pending a full investigation of the incident.

Two days after the incident the various representatives arrived in Bahrain. Boeing and Qantas Engineering at Mascot sent teams of structural engineers to assess whether the aircraft was still airworthy. The Australian Government sent Department of Transport investigators. The aircraft had suffered some damage which included rippling of the fuselage skin around the rear doors and on the overwing surfaces. A considerable number of the inspection panels had 'popped' all over the skin, with their spring loaded locks still in the 'locked' position. Internally a few rippled hatracks were discovered.
 
Boeing estimated that at the time of the incident the aircraft weighed about 211,000 pounds (96,000 kgs). If the weight had been 250,000 pounds (114,000 kilograms) instead of 211,000 pounds (96,000 kilograms), the factored ‘G’ weight with the sustained 4.57G, would have been around 1,144,000 pounds (520,000 kilograms). There would have been no way that the aircraft would have remained intact. It would have disintegrated at about 25,000 feet (7,600 metres).

Some days later the Captain got a call from one of the instrument engineers saying that he thought he had duplicated the fault, and would the crew come out to the airport. The crew went out to the hangar where VH-EAB was parked. The electrical engineer went down into the Lower 41 section, an area below the flightdeck,  where all the electrical equipment is situated. After much fiddling he called out from the depths of the aircraft, 'Is that what you saw?'

The captain looked at his artificial horizon and saw that it was now indicating 30 degrees of bank to the right, the standby horizon was indicating straight and level as was the First Officer’s instrument. The ‘clacker’ was sounding and the light on the instrument panel was flashing, indicating the difference between the two dials. When asked what he had done to replicate the instrument readings, the crew were told that there was a loose wire in the power source to the Captain’s horizon instrument. The Captain agreed that the fault had been duplicated, and the mystery of what had caused the instrument to malfunction was solved.

So the cause of the incident had been found but what had actually happened? Sometime after everyone got back to Sydney, the data in flight recorder had been analysed and the readout was available. I quote in part from the official report.

INTERPRETATION.

3.1. Prior to the incident the aircraft was nominally at Heading variation between 2600 and 2800 occurred, probably 35,000 feet at a indicated speed of 277 knots (M.810). Associated with passage over Jiwani.

3.2. Immediately prior to the height loss, the tape height was 35,700 feet. The heading changed from 2800 to 2750 degrees where the rate of turn increased to about 20 / second. By 2600 the bank angle would have been in excess of 400 to the left.

3.3. A rapid altitude loss followed, increasing in rate with time in the first half of the episode. It was later calculated that the rate of descent had reached 84,000 feet per minute at one instant. Height loss was arrested at 16,800 feet about 40 seconds after the start. During this the Indicated airspeed increased from 277 knots to 475 knots; and the “G” was more than 1.0 throughout. It was 3.0G in 20 seconds and exceeded this for a further 17 seconds, peaking at 4.57G. (the aircraft had an effective weight of 965,000 pounds - Maximum allowed 336,000 pounds). It was 2.5G when level in the pullout. The heading at pullout was approximately east, having changed 1800 through south from west.

3.3. The sustained high G began to exceed 1.0 immediately the descent  commenced, and was maintained until after the descent was arrested.

3.4. This implies a tight spiral or pitching in the vertical plane. It was probably a combination of both and mainly pitch in the final pullout. The “G” factored “weight” must have exceeded 600,000 pounds for much of the descent, and there must have been fairly severe buffet.

3.5. There is however, indication that heading was relatively constant during the pullout which “bottomed” at 16,800 feet. At this point the maximum speed during the incident of 475 knots indicated was being approached, being the equivalent of M.93. At this speed position error tends to be asymptotic and the speed would have been faster.

3.6. Having achieved the pullout on a relatively steady heading, the aircraft ascended from 16,800 feet to 21,500 feet while the ‘G’ decreased from 2.4 to normal 1.0 to -0.63 at 21,500 feet. The aircraft started to descend again.

3.7. A condition of zero to negative G (-0.63 maximum) occurred in the roundover above 20,000 feet for about 10 seconds.

3.8. A second dive on a fairly steady heading returned the aircraft to a further pullout at 17,000 feet giving +2.0 G. This pull-up caused a climb back to 20500 feet where relatively level flight was established.

Total time of the incident to this point was 2 minutes.

(The above report was courtesy of Qantas Airways).

So that was what happened on that fateful night, but there still remained the question of how and why it happened. Like all accidents or major incidents, it was a series of events that combined to create a situation.

The first link in the chain of events was the faulty instrument. A long time later, a Flight Engineer informed the First Officer of a momentous event that occurred about six months before the incident when he was an apprentice electrical engineer. He was a very clever individual, and a top class Flight Engineer who, during his course, discovered that there was a basic flaw in the electrical wiring design of the Boeing 707’s artificial horizon. He found that if a certain fault occurred in the wiring of the instrument it would indicate 30 degree right bank with no warning flag.

He went to great lengths to get the problem fixed but to no avail. If the wiring defect had been corrected then the incident would never have happened. The first link in the chain had been forged.

The second link was that none of the pilots knew of the previous history of intermittent faults in the instrument. Obviously, in retrospect, there was an omission in the co-operation between crew members. Engineers would inform the Captain of major items of interest to them, but nothing of an engineering interest would be passed on. In those days this was standard practice. Nowadays all pilots and flight engineers go through the ‘Technical Log’ and ‘Notices to Crew’ with a fine tooth-comb. If some mention had been made of nuisance comparison warnings between the two artificial horizons, then maybe, when the defect happened, the actions to control the aircraft would have been different. The second link had been completed.

Then there was the weather. It was pitch dark with no moon and, at the time of the incident, there was some light turbulence. There was no natural horizon outside so control of the aircraft depended solely on the flight instruments. If there had been a natural horizon, quite obviously control of the aircraft would have been easily maintained with outside reference without the misleading information on the flight-deck. The third link had been made.

As the aircraft passed over Jiwani, the Second Officer, who was in the right hand seat at the time, was sending the position report to Karachi. In those days part of the communication equipment was the ‘bit of tin’. This was a piece of medium gauge aluminium, approximately A4 in size, with a couple of alligator clips attached to hold the Airep, a met report, and the flight plan together with the deck log. The latter two were used to monitor the progress of the flight.

As the Second Officer was sending the report, he had hold the ‘bit of tin’ in the beam of the map light, and as a result, his instrument panel was obscured. As the aircraft rolled to the left he was still sending the position report. When the over-speed warning started and he saw his instrument panel, he could see that the aircraft was almost inverted, and in a steep dive. This was corroborated by the standby instruments. The Captain’s instruments still indicated a level turn to the right.

At extreme attitudes the artificial horizon indications are notoriously difficult to interpret, so it would not have been unreasonable to have initially thought that all three instruments were error. However, if he had seen the start of the manoeuvre there would have been no difficulty on his part to prevent the episode in the initial stage. Consequently the fourth link had been manufactured.

The comparison warning was fitted on the aft centre console between the pilots. When the warning went off, the Captain looked down and slightly behind him to check what was occurring. The warning was probably cancelled and when he looked back at his instrument panel he saw that the aircraft was now in a 30 degree bank to the right with no warning flags on any instrument. As the auto-pilot was disconnected the aircraft was rolled to the left to correct the indicated right bank. In fact, the aircraft had been flying straight and level, but was now rolling to the left with the instrumentation still indicating a turn to the right. More left aileron was applied until the aircraft was almost inverted and in a steep dive. If, in that fateful second, the Captain had not looked away to check the warning, and had seen the fault instantly manifest itself, he would have immediately rejected the indication as impossible for the aircraft to achieve, and done nothing as it was only an indication fault. Now the final link in the chain was complete.

Qantas eventually sent the flight crew back to Sydney as passengers, for they were still held 'out of service' pending the outcome of the Board of Inquiry. They were all treated very much like lepers as nobody wanted to talk to them for fear of being contaminated with their 'bad luck'. 

After the flight data recorder was transcribed into its various sections so it could be analysed and understood by all parties involved, the crew were told the result of the Board's deliberations.

The Captain had to do some extra training. The Second Officer and the Flight Engineer were absolved of any wrong doing, while the First Officer was reprimand for reducing the cruise speed back to a 'least load speed', a difference of only 27 knots!

Footnote: On July 24, 1969 Qantas upheld an appeal by the AFAP on behalf of the First Officer against his reprimand. It had only succeeded by the most persistent efforts of Bert Smithwell and his AFAP team, and culminated in a trip to Canberra by them to lobby the Minister of Civil Aviation, Senator Cotton.

The aftermath of this incident had a somewhat less satisfactory result in one sense. The captain did some more training. However after many tyres deflated on completion of a landing on a short sector flight from Kuala Lumpur to Singapore, his retraining was terminated and he became a First Officer. He later took early retirement and returned to ‘civilian’ life. There was a rumour that went round that Sir Roland Wilson, who was Chairman of the company at the time, and a banker, had decreed that the captain was never to be given command of a Qantas aircraft again. If this was true, then perhaps an even greater injustice was done! 
 

In closing - I'm reminded of that famous saying ... 'If it ain't a Boeing then I'm not going!!!'

March 2022.