Single Generator Ops on A319/A318/A320/A321 etc

[TheShadow]

With respect to the incident below, please complete the following thought:
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In many twin-engined airliners it is considered acceptable under the minimum equipment list concept (MEL) to press on once a generator is declared unserviceable. By "press on", here we mean for the next crew to accept the aircraft on the basis that the APU generator and the remaining engine-driven generator are mutually in support of each other. This is fine in theory unless of course it's a feeder fault or bus-tie defect that can kick another generator off-line..... as seems to have happened here.
In densely populated airspace or even just over the sparsely populated airspace of the Amazon it's almost inconceivable that a modern airliner can be without communications. In an A320/A319/A321/A318 type aircraft it's inconceivable that one could survive in instrument conditions/at night without an operating generator. In fact, in daylight/blue sky conditions that wouldn't be conceptually possible in a FBW jet........
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G-EZAC
Type: Airbus A319-111
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Summary:
The aircraft was dispatched under the provisions of the operator’s Minimum Equipment List with the Auxiliary Power Unit (APU) generator on line, substituting for the No 1 main generator which had been selected off after a fault on the previous flight had caused it to trip off line. During the cruise, the APU generator disconnected from the system, probably because of a recurrence of the original fault. This caused the loss of a substantial number of aircraft services, including some flight instruments and all means of radio telephony (RTF) communication. Manual reconfiguration of the electrical system should have recovered many of the services but the flight crew was not able to achieve this. Since they were without RTF communications, the crew considered that the best option was to select the emergency transponder code and continue the flight in accordance with the flight plan. In the light of the initial findings of the investigation, four safety recommendations are made. The investigation is continuing.
Download report:
S9-2006 G-EZAC.pdf (389.25 kb) (http://www.aaib.dft.gov.uk/cms_resources/S9-2006%20G-EZAC.pdf)

[john_tullamarine]

Can't offer any Airbus comments .. however .. the MEL is not a system for permitting cavalier continuation of flight.

The basic philosophy is that the aircraft Type has a bunch of kit necessary for certification .. ergo, if a bit of kit is broken, the aircraft is unairworthy.

That's all fine and beaut .. but, in the real world, it is not very workable unless you are a well-heeled private operator who doesn't really need to fly unless everything is gold plated.

Therefore, the gurus have a think tank and consider a range of broken kit .. with the aim of determining what additional limitations, etc., are appropriate for flight to continue while maintaining something akin to the basic certification risk profile. As a simple example, if a cabin item doesn't function, there might be some limitations imposed on passenger operations. At the end of this process, we have the MMEL, authorised by the certificating Authority with the OEM's blessing. The MMEL then is modified to address any specific hull and local regulatory requirements .. when this is finished the local Authority approves the modified MMEL as the operator's MEL.

The important thing to keep in mind is that the MEL addresses intentional operation with a bit of busted kit and seeks to maintain the certification risk levels.

It is a different matter when something breaks after despatch .. in this case it makes sense to have a look at the MEL to see what considerations might be relevant for the Commander to take into his decision making process. However, the inflight situation is managed as a one-off risk control and mitigation situation.

[TheShadow]

Might have expressed myself poorly here.
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Looking more at the supposition that because a generator keeps tripping off line that there's something wrong with said generator - so "no problems, we'll keep operating that bird with the APU running until it gets back to home-plate and we can address it further". In this case the fault was beyond the generator and in the circuitry (bus-tie?) and tripped the APU generator off line. You've then got an FBW a/c enroute in IMC/at night with only one generator up and running.
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Is that acceptable? Is it survivable with FBW if that fault was to cause another event? Or do we/are we use(ing) an ETOPS style of philosophy and simply declare that "you'd have to be mighty unlucky for that last remaining generator to quit on you. Statistically speaking it just ain't gonna happen. We got the figures to prove that."
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Well I'd be prepared to debate the validity of any such statistics when it comes to a singular (non-redundant) electrical distribution system - no matter how many generators are hanging off of it and supplying it. It smells a bit unsafe to me - and not just because of the FBW nature of the named airplane brands. And just because we've been doing it for years doesn't necessarily mean that it's a valid philosophy.

[john_tullamarine]

I suspect that the original MMEL/MEL may have been misused/misinterpreted to despatch the aircraft ? The workup of the documents should have given enough guidance to distinguish between component and other aspects of the overall system.

[Jazbag]

A similar thing happened in our airline to me (DC Bus 2 fail) luckily we found it was a defective relay. Aircraft did not have AC Ess and DC ESS because of the malfunction of this relay.

[john_tullamarine]

.. I guess that one of the salient messages in this thread is that one should not approach MEL use with mind in neutral ... a bit like the early days of EFIS and FMS etc ... we never trusted anything on first consideration ... a healthy dose of distrust has saved many an airman's life over the years ...

When considering MEL permissions the pilot must consider the big picture and always try to play a bit of the devil's advocate .. after all, if you take the bird, it is YOU up there in the tube when it all turns to custard ...

[PantLoad]

Further, regarding the MEL issue, is that of time limits to effect repair. It seems to be more and more prevalent, these days, to make the repair (and remove the MEL) toward the end of the legislated maximum time interval, as opposed to "As Soon as Possible" (which is what's required under law).

What really pushes the envelope of MEL law is to issue an MEL so as to defer routine maintenance. This, of course, is illegal, but many carriers seem to be getting away with it.

For those of us who remember, a man named Frank Lorenzo (I suppose, in a way, we should thank him.) so far exceeded the bounds of law, due diligence, etc., that the MEL rules were changed to what we have today, worldwide. Some middle-management maintenance people (Eastern Airlines...thanks to ol' Frank) actually served time in a federal prison in Atlanta for some of these dirty deeds.

John is quite correct in his wisdom that we, as pilots, need to take a few steps back and view the big picture. This, along with strict adherence to MEL law, intent. and philosophy, will circumvent 'surprises' like those described, initially, in this thread.


PantLoad