Originally Posted by
Capot
...I was there when, still sitting in the flight deck at Muharraq , the Captain of a B707-338C, operating as QF739 on February 21, 1969 explained how he regained control after the aircraft went out of control over the Arabian Gulf on route to Bahrain at FL350 and M 0.81, dived inverted, rolled, probably went supersonic momentarily (not recorded accurately due to compressibility issues at the pitots) ) recorded +4.57G and - 0.63 G, and lost 19,000 ft. "I realised that we had finally entered a spin", he said, "so I recovered it like I would a Tiger Moth. No big deal." And off he went with the crew for a stiff drink in the Gulf Hotel. We found soap stuck to the ceilings in the toilets. Crews would be trained to recognise a situation where they have lost effective control of their aircraft because they do not understand what the automatics are up to, and/or when something is obviously seriously wrong and getting worse, and to use the button to recover, stabilise, whatever, using their basic flying skills, if they have any.
The Qantas Boeing 707-338C VH-EAB was operating the scheduled service Sydney - London as QF739 on February 21, 1969. On the sector Bangkok - Bahrain it had 72 people on board. On departing Bangkok the aircraft was approximately 20 tonnes under its maximum take-off weight. It was this fact 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 passenger cabin was in darkness and the Tech and Cabin Crew had started rotating for their meal breaks. The Captain was back on the flight deck, having finished his meal break while the First Officer was in the Crew Rest Area, just starting his.
The aircraft was stabilised in normal cruise mode, travelling at 35,000 feet and 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.
Unbeknown to the pilots, the aeroplane had a recent history of problems with the Captain's Horizon Direction Indicator, or Artificial Horizon (HDI), which was ultimately attributed to a faulty Bendix gyroscope.
The post incident investigation recorded that the Captain had glanced away from his main instruments, down and to his right, at the centre pedestal.
When he looked up he immediately 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 M 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 FDR recorded a maximum positive 'G' figure of 4.57 while a significant negative 'G' figure of 0.63 was recorded.
There were a couple of 'porpoising' manoeuvres undertaken as the Captain and Second Officer recovered the jet, and given the speeds and 'G' indications, it was fortunate they didn't have the wings and tail fail in the process. As it was, there was a significant 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.
Boeing estimated that at the time of the incident the aircraft weighed about 96,000 kgs.
Multiplying this by the positive 'G' vale of 4.57 indicates that for periods during the 'upset' (such is the euphemism used for events of this nature) the aircraft 'weighed' some 440,000 kgs or nearly 40 tonnes more that a fully laden Boeing 747-400.
The aircraft was successfully landed at Bahrain Airport without further incident. The Tech and Cabin Crew were stood down as is normal following this sort of misadventure while the passengers were dispersed to Gulfair and British Airways to continue their journey. Teams of engineers were dispatched from Boeing and Qantas Engineering at Mascot to assess whether the aircraft was still airworthy.
The Bahrain Bomber Incident
I didn't know the Capt but I know the SO of that event, and the report. Airplane didn't spin...it did an impressive spiral dive however. At that time the aircraft did not have a comparator between attitude indicator other than pilot monitoring. IIRC while the B747 had comparators early on, it wasn't early enough for the AI 855, a B742 off the end of 27 at Mumbai, and it wasn't insistent enough for the KAL 8509, a B742F out of Stanstead. IN both of these cases, the FE was aware of the instrument failure, and despite hving a comparator in the second event, it was not enough on the night to save the flight from the disorientation of an erroneous AI.