Archives For Safety

The practice of safety engineering in various high consequence industries.

Another A320 crash

25/03/2015 — 4 Comments

Germanwings crash (Image source: AFP)

The Germanwings A320 crash

At this stage there’s not more that can be said about the particulars of this tragedy that has claimed a 150 lives in a mountainous corner of France. Disturbingly again we have an A320 aircraft descending rapidly and apparently out of control, without the crew having any time to issue a distress call. Yet more disturbing is the though that the crash might be due to the crew failing to carry out the workaround for two blocked AoA probes promulgated in this Emergency Airworthiness Directive (EAD) that was issued in December of last year. And, as the final and rather unpleasant icing on this particular cake, there is the followup question as to whether the problem covered by the directive might also have been a causal factor in the AirAsia flight 8501 crash. That,if it’s the case, would be very, very nasty indeed.

Unfortunately at this stage the answer to all of the above questions is that no one knows the answer, especially as the Indonesian investigators have declined to issue any further information on the causes of the Air Asia crash. However what we can be sure of is that given the highly dependable nature of aircraft systems, the answer when it comes will likely comprise an apparently unlikely combinations of events, actions and circumstance, because that is the nature of accidents that occur in high dependability systems. One thing however is for sure, there’ll be little sleep in Toulouse until the FDRs are recovered, and maybe not much after that….

Postscript

if having read the EAD your’e left wondering why it directed that two ADR’s be turned off it’s simply that by doing so you push the aircraft out of what’s called Normal law, where Alpha protection is trying to drive the nose down, into Alternate law, where the (erroneous) Alpha protection is removed. Of course in order to do so you need to be able to recognise, diagnose and apply the correct action, which also generally requires training.

MH370 underwater search area map (Image source- Australian Govt)

Bayes and the search for MH370

We are now approximately 60% of the way through searching the MH370 search area, and so far nothing. Which is unfortunate because as the search goes on the cost continues to go up for the taxpayer (and yes I am one of those). What’s more unfortunate, and not a little annoying, is that that through all this the ATSB continues to stonily ignore the use of a powerful search technique that’s been used to find everything from lost nuclear submarines to the wreckage of passenger aircraft.  Continue Reading…

Here’s an interesting graph that compares Class A mishap rates for USN manned aviation (pretty much from float plane to Super-Hornet) against the USAF’s drone programs. Interesting that both programs steadily track down decade by decade, even in the absence of formal system safety programs for most of the time (1).

USN Manned Aviation vs USAF Drones

The USAF drone program start out with around the 60 mishaps per 100,000 flight hour rate (equivalent to the USN transitioning to fast jets at the close of the 1940s) and maintains a steeper decrease rate that the USN aviation program. As a result while the USAF drones program is tail chasing the USN it still looks like it’ll hit parity with the USN sometime in the 2040s.

So why is the USAF drone program doing better in pulling down the accident rate, even when they don’t have a formal MIL-STD-882 safety program?

Well for one a higher degree of automation does have comparitive advantages. Although the USN’s carrier aircraft can do auto-land, they generally choose not to, as pilot’s need to keep their professional skills up, and human error during landing/takeoff inevitably drives the mishap rate up. Therefore a simple thing like implementing an auto-land function for drones (landing a drone is as it turns out not easy) has a comparatively greater bang for your safety buck. There’s also inherently higher risks of loss of control and mid air collision when air combat manoeuvring, or running into things when flying helicopters at low level which are operational hazards that drones generally don’t have to worry about.

For another, the development cycle for drones tends to be quicker than manned aviation, and drones have a ‘some what’ looser certification regime, so improvements from the next generation of drone design tend to roll into an expanding operational fleet more quickly. Having a higher cycle rate also helps retain and sustain the corporate memory of the design teams.

Finally there’s the lessons learned effect. With drones the hazards usually don’t need to be identified and then characterised. In contrast with the early days of jet age naval aviation the hazards drone face are usually well understood with well understood solutions, and whether these are addressed effectively has more to do with programmatic cost concerns than a lack of understanding. Conversely when it actually comes time to do something like put de-icing onto a drone, there’s a whole lot of experience that can be brought to bear with a very good chance of first time success.

A final question. Looking at the above do we think that the application of rigorous ‘FAA like’ processes or standards like ARP 4761, ARP 4754 and DO-178 would really improve matters?

Hmmm… maybe not a lot.

Notes

1. As a historical note while the F-14 program had the first USN aircraft system safety program (it was a small scale contractor in house effort) it was actually the F/A-18 which had the first customer mandated and funded system safety program per MIL-STD-882. USAF drone programs have not had formal system safety programs, as far as I’m aware.
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SR-71 flight instruments (Image source: triddle)

How a invention that flew on the SR-71 could help commercial aviation today 

In a previous post on unusual attitude I talked about the use of pitch ladders as a means of providing greater attensity to aircraft attitude as well as a better indication of what the aircraft is dong, having entered into it. There are of course still disadvantages with this because such data in a commercial aircraft is usually presented ‘eyes down’, and in high stress, high workload situations it can be difficult to maintain an instrument scan pattern. There is however an alternative, and one that has a number of allied advantages. Continue Reading…

Unreliable airspeed events pose a significant challenge (and safety risk) because such situations throw onto aircrew the most difficult (and error prone) of human cognitive tasks, that of ‘understanding’ a novel situation. This results in a double whammy for unreliable airspeed incidents. That is the likelihood of an error in ‘understanding’ is far greater than any other error type, and having made that sort of error it’s highly likely that it’s going to be a fatal one. Continue Reading…

A while ago, while I was working on a project that would have been based (in part) in Queensland I was asked to look at the implications of the Registered Professional Engineers Queensland act for the project, and in particular for software development. For those not familiar, the Act provides for the registration of professional engineers to practise in Queensland. If you’re not registered you can’t practice unless you’re supervised by a registered engineer. Upon registering you then become liable to a statutory Board of Professional Engineers for your professional conduct. Oh yes and practicing without coverage is a crime.

While the act is oriented squarely at the provision of professional services, don’t presume that it is solely the concern of consultancies.  Continue Reading…

AirAsia QZ8501 CVR (Image source - AP Photo-Achmad Ibrahim)

Stall warning and Alternate law

According to an investigator from Indonesia’s National Transportation Safety Committee (NTSC) several alarms, including the stall warning, could be heard going off on the Cockpit Voice Recorder’s tape.

Now why is that so significant?

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