QANTAS flight QF 32 – Media versus Reality

When something spectacular occurs the media tends to bring out all the hype – aircraft crashes, disaster narrowly averted, Airbus unsafe, or hero pilots save the day. Reality is not like that. Instead we should be praising the design standards that are current in civil aviation. So, what are some of the safety precautions that are hidden from the public gaze?
First, all aircraft engines are tested extensively to ensure that they can contain a fan or turbine blade if it breaks off. Next, all aircraft are designed with multiple redundancy in their various systems. Thirdly, flight crew are well trained and routinely tested on the whole gamut of emergencies. So, what do we know about the uncontained engine failure that occurred on QF 32 out of Singapore bound for Sydney?

Engines are tested to prove that they are able to contain fan and turbine blade failures  but it is impossible to contain the huge energy should a turbine disk break when rotating at 12,000 rpm. If this was done the casing would be so heavy I doubt the aircraft would be able to fly! Instead the answer is to build the turbine discs so that they don’t fail. Nevertheless sometimes (very rarely) they do, and it rather looks as though this is what happened to QF 32.
The A380 comes fitted with either RR Trent engines (the Trent 970 on Singapore Airlines and Lufthansa, the Trent 972 on QANTAS) or the Engine Alliance (EA) GP 7270 on Emirates and Air France. Therefore, despite what the media has been printing it is not an aircraft problem but a specific engine problem. The Trent RR 972 is mechanically the same as the 970 but its electronic control system allows a slightly higher power, whether this has had something to do with it I don’t know. Singapore and Lufthansa have inspected all their engines and have not grounded their aircraft, but QANTAS have found some ‘anomalies’ with the Trent 972. Again, whether this is significant or not I don’t know.

Next, an Airworthiness Directive (AD) has been published by EASA requiring extra inspections regarding wear on the abutment faces of the splines on the IP shaft rigid coupling. These things are not unusual, but we don’t know yet whether this has any bearing on the uncontained failure on QF 32. However, it is just possible that rearward movement could have resulted in damage to the bearing chamber oil seals, causing an oil leak, followed by an oil fire, which in turn over-temperatured the turbine blades causing them and then the disc to fail.
It is still much too early to know what is the cause, and one has to be very careful when trying to guess what may have happened. Turbine disc failures are very, very rare. In this case, the 74 dollar questions are (a) is this a basic design fault – possible but very unlikely; (b) is it a manufacturing fault in the turbine disc – slightly more likely since only a very slight flaw in the metal can cause a fatigue fracture; (c) is it related in some way to the AD and the wear on the splines – seems rather more possible; (d) is it a maintenance error – could be, but unlikely as RR do the maintenance; (d) is it related to the difference between the two versions of the Trent engine – possibly, but I don’t know; (e) or is there something in Qantas operational procedures that is different to other airlines – it has been known to happen.
I stress again that turbine disc failures are very, very rare. But even so the aircraft manufacturer designs the systems so that there is multiple redundancy and the aircraft will still fly despite heavy damage. There is no doubt that Airbus has done a good job. It is important to note that the high energy part of the engine (the turbine discs) are forward of the main wing spar and thus forward of the fuel tanks. The main damage to the wing which you can see in the first of the pictures below is in the very thin structure ahead of the main spar and are not load bearing. However I am slightly concerned about the damage indicated by the aft of the two arrows which appears as though it could be behind the spar. All will come out in the wash when the various authorities, Rolls Royce and Airbus examine the damage.

Clearly, the QANTAS crew handled the whole thing very professionally, as you would expect, QANTAS is a good airline.
And the aircraft performed as expected, all 4 engine aircraft fly very well on 3 engines, and can even do so on 2. The problem is that when something like this happens other systems are always damaged to a certain extent. For example they must have lost a hydraulic system because the aircraft landed with the undercarriage doors left down, but again the aircraft is designed to cope with this. And they also had difficulty in shutting down the No 1 engine (the outboard one on the same wing) after landing, which indicates that some of the control wiring that runs down the leading edge of the wing must have been damaged too. However, the crew were not that worried as the passengers all left quietly via the steps and an evacuation was not needed.
As I said earlier, other manufacturer’s engines have suffered these failures too. Many readers will remember the DC10 that landed at Sioux City after the centre engine failed in a similar manner. Severe damage was done to all the hydraulics such that the crew were left with no working control surfaces and had to land the aircraft using differential engine thrust alone. All engine manufacturers have experienced similar failures – Rolls Royce is not alone.
For example, here is a picture of what happened to an American Airlines B767 a few years ago when the turbine disc on the GE CF6 engine burst during a ground run at full power. The crew had reported a problem on the inbound sector and the engineers were doing checks.

So, what points am I trying to make. First, however carefully manufacturers design engines, and however good a job they do, we must realise that it is extremely difficult to prevent all failures. Second, the effect of those failures that do occur can be, and are, mitigated by good aircraft and system design – clearly Airbus have done a very good job. Thirdly, good flight crew training pays off. Instead of listening to media hype we should be celebrating Airbus’ good design and engineering!