The ATSB has described how an ‘irregularity’ in the elevator control system hit QF 72 while it was in level flight at 37,000 feet over WA yesterday shortly before its emergency landing at Learmonth with dozens of injured passengers.
In lay terms the elevators are control surfaces on the tail of the jet which are critical to stable flight.
The ATSB said today that the pilots “received electronic centralised aircraft monitoring messages relating to some irregularity with the aircraft’s elevator control system.”
The jet with 303 people on board then climbed about 300 feet above its intended flight level where the crew began following the non-normal checklist response actions.
Julian Walshe the ATSB’s director of air safety investigations said “The aircraft is then reported to have abruptly pitched nose down.”
The obvious lines of inquiry for the ATSB now include reviewing any history of faults with this particular A330, and its maintenance history, which should include routine records of parts replacements and other relevant repairs, as well the responses the aircraft made to pilot actions as they brought it under control and then landed it at Learmonth.
It is also now abundantly clear that the aircraft dived very steeply and quickly and for many thousands of feet before it returned to near level flight and landed.
This inquiry will be of the highest interest to other operators of the A330 type as well as Qantas.
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Passengers interviewed on ABC radio Perth this morning reported that there were two descents with a brief intervening period of level flight, and that the subsequent flight to and landing at Learmonth was a bumpy ride. Consistent with the first descent being triggered by the electronic systems (perhaps a faulty depressurisation alert causing autopilot emergency descent?), pilots regaining manual control then reactivating electronic systems, only to have electronic systems trigger a second descent, and then flying manually to Learmonth. Presumably the PAN PAN was issued after the first descent and the MAYDAY after the second.
Peter,
Yes the distress calls were made in the order, with Mayday indicating the pilots believed the structural integrity of the jet was at risk. Something happened during that brief period of stable flight to throw the jet into another dive. I understand there will be a detailed investigation into the responses of the Airbus control system to the pilot inputs and whether or not they followed the optimal course of action.
This inquiry is not about blame, but understanding why something happened, and whether or not in the aftermath of a very serious incident there are changes or improvements that should be made to the operating procedures they were trained to use in such circumstances or the systems themselves.
I was flying my light aircraft PER-BRM yesterday at FL135 when the emergency call came through at around 12.52. The call to melbourne Centre was a PAN call not a MAYDAY call, a PAN call is less serious and urgent than a MAYDAY. The pilot appeared to be reporting an issue with the computerised flight controller and that he was diverting to Learmonth. In a further exchange he reported that he thought there were injured pax up the back and a subseqent call requested medical assistance at learminth. During the PAN call he appeared calm but his voice had a degree of stress in it which you would expect given the apparent event they had just been through. I didn’t hear the rest of the radio transmissions as they switched to another frequency, I can only assume that a MAYDAY call didn’t follow the PAN call. These events invoke lots of emotion, the real emotion should be for the pilots who got the aircraft stable (irrespective of what happened) and landed it safely. For this they should be highly commended. Anyone flying and not keeping their seatbelt fastened at all times (other than toilet visits) should take this incident on board. I wonder how many injuries could have been avoided during this event if everyone was securely fastened. One last point, in today’s West Australian headline screamed “8,000 feet in 10 seconds”. A descent rate 48,000 fpm and the wings stayed on, I don’t think so, this is absolute nonsense reporting by the journalist.
There has been speculation as to whether the Defence radar transmissions nearby QF72 may have caused the plunge… or if it is a ’software/systems bug’ in the Airbus auto-pilot control logic.
However, I received the following from NATS (UK equivalent of CASA) on that speculation.
I’ll start with some very simple assumptions, then we’ll see if there are any major errors in those assumptions.
Published frequency 19.8 kHz, say 20 kHz = wavelength 15 km.
Published power 1 MW (1,000,000 Watt = 10^6 Watt). Let’s assume this is radiated power rather than the transmitter power.
Transmitter is a “point source”, radiating evenly into a hemi-sphere above the station.
Aircraft at 11 km high (36000 ft) and a slant range of 16 km (45° above the horizon).
Aircraft is a 777, which we can consider as a 60 m long and 6 m thick cylinder, presenting at most a surface of 360 m² to the transmitter.
Surface of the hemi-sphere = 2 * pi * r^2 = 6.3*(16000)^2 = 1600 * 10^6 m². With 10^6 Watts radiated, the power at location of the aircraft is 1/1600 W/m², so the entire aircraft structure intercepts about 0.225W, about 1/6th of the power of the bulb in a typical flashlight/torch.
I’ll have to leave it to an antenna expert to tell us exactly what voltages and currents are induced in a cylinder that is a minute fraction of the wavelength, how much will be simply dissipated in the skin (skin effect, Faraday cage effect) and how much of it would be detectable inside.
One of my assumptions is that the transmitter radiates evenly into a hemisphere. In practice, we see huge antenna farms on the photos, with dimensions in the order of half a wavelength, so we can expect the radiation to be at least somewhat directional in both the horizontal and vertical plane. But it seems unlikely to me, that gains of more than 3 to 4 are obtained in any one direction.
My other assumptions of course are the actual distances: 16 km slant range and 11 km height and 45° above the horizon. Since there is an r_squared involved, reducing the slant range to 11 km will roughly double the power. I haven’t done that because usually the “overhead” power of a transmitter installation is less than that at lower radiation angles.
So OK, even if I’m out by a factor 10 or so, the total power arriving on the skin of the entire aircraft is still about that of the bulb in a flashlight. Only a fraction of that will get “inside”. To actually affect the electronics (not the radio, but the electronics such as the ADIRU), something already has to be very seriously wrong with those electronics.
Let me add some anecdotical “evidence”.
Have a careful look at the forward part of the fin [photo of early Concorde attached]. See the two green-brown vertical “slashes”? They are indeed two “slashes” into the metal structure, covered by “radio-transparent” fibreglass, and for some reason never painted over until nearly the end of the flight test programme. They are there on all Concordes, but painted over on the others.
They are the HF (high-frequency) slot antennas.
In the olden days, a wire strung from the cockpit back to the fin would do the job, but that wasn’t really acceptable in the supersonic era….
But a slot cut into a metal structure, closed on the inside, and connected to a radio transmitter, will radiate HF energy.
So that was the solution on Concorde, and you will find similar solutions on most present-day airliners.
However…. a radio engineer will tell you that such a slot aerial at HF frequencies is not exactly the most efficient, and will set up very high high-frequency currents in the surrounding structure.
As happened on Concorde.
So…. here we had an 100W HF transmitter, directly connected to the airframe, and trying to radiate at least some of its energy…. but some it just got dissipated in the structure (SWR not quite one, for the experts).
As it so happened, the yaw rate gyros, part of the autostab system, were mounted precisely in this area.
Guess… when we started to test the HF radios on longer-range flights, we found the tail wagged and twitched a bit whenever somebody talked on the HF radio….
Even so, it took us some time to correlate the twitches with the autostab. A small filter solved the problem.
Moral of the story?
Nearly forty years ago it took us 100W injected directly into the structure of an aircraft (still being flight tested, mind you) to provoke a mere ‘twitch’ in an analog control system.
Less than a milliWatt/m² of VLF impacting on an aircraft, from a facility overflown regularly, and suddenly causing a malfunction in an electronics unit (ADIRU or AoA sensor)? Try another one, this one has bells on.
Graeme Harrison