GAM Aero Commander nose gear failure
 

Howdy experts,

I just watched the crew do an outstanding job of landing on R 26 at YMEN with an unsafe nose gear. It collapsed as expected.

My question is to the shutdown feathering of the Engines, I understand normally Garetts aren’t feathered on shutdown but why was there smoke and flames on feathering this time? Did they forget to shut off the fuel first and it melted down? (A little like on the old F-27 ( RR Dart fixed turbine ) if you didn’t engage the prop locks after landing it would quickly over temp and melt down…)

https://www.9news.com.au/national/es...2-f13e05b064d7

just curious.

I've seen the odd hot start... but never a hot stop :E

Looks a lot like the by product of pulling the stop and feather/emergency stop function on a Garrett. The engine doesn't have the chance to purge the combustion chamber, so a fair bit of unburnt fuel I'd suggest from my very basic, engine goes brum brum level of knowledge. Happy to stand corrected.

J3 you are correct as they do tend to do that on an emergency shut down. I double check the rigging first to see the fuel shuts off first before the feather valve.
It is also part of my engine run after maintenance when called up. I always put the prop back on the locks, spin it and restart it to eventually do a normal shut down

I think you mean torching when oldmate doing the start is too busy gasbagging and forgets to introduce spark quick enough after fuel input. Hot start will just melt your hot section, not nes a flame thrower, could be a lot of black smoke if you don't deal with it.

Flash of flame like that is exciting but does nothing much as its too quick to harm anything.

Interesting. In my 40 years of flying turbine engines of many different types, they have all had the spark operating before fuel is introduced. Listen to any turbine starting and you will hear the igniters shortly after starter engagement (PT6 is a classic example).

I've yet to encounter an engine where the pilot controls the spark, but I'm happy to be educated.

Saab mate, fuel introduced prior to ignition on because austronauts.

Don't think I'd taker an aircraft with a certain gear problem from an airfield with high RFF to an airport with no RFF. Not right or wrong - just my preference for the
likelihood of the unexpected in this situation.

43 inches I'm intrigued. Never flown a Saab, but is it correct that the pilots manually select ignition after the fuel goes in?

It's some sort of left over from the A model having clockwork engine electrics. The SAAB has an auto start system where you can just hit start with levers in the right position and it does the rest. But certain operators felt it had issues so they use a motoring start where you put the fuel in start once reaching an Ng threshold and then ignition to auto, AFAIK it's only an Australian thing. One excuse I heard was that it reduced torching, but the technique seems to be in favor of torching if you think about it, in any case the B model has a digital system, so much more refined and reactive to changes.

Pretty sure the Irish Concorde, needed the ignition to be manually selected in the start sequence on the PT-6.

That's what I though as well.

Could also be in breach of CASR Part 91.685, I'm sure our friends at CASA are onto it.

I assume the diversion had a lot to do with their maintenance base being at Essendon.

Thanks 43 inches, most interesting.

Breach of 91.685 is an interesting discussion.

Hypothetically, an aircraft has a nose gear failure leaving Adelaide but can climb and cruise happily with the failure. Drag and fuel burn not an issue.
Is it in breach of 91.685 if it continued with the pax on board to Mel - and for arguments sake, both airports CAVOK and same RFFS.

The aircraft had a groundspeed over 300kts between ADL and MEB so I guess that would indicate the gear was up for that leg?

You really have no idea. Essentially everything you said is incorrect. It’s not an A model hangover. It’s not just Australian operators.

It’s in the AOM FFS. The manufacturer recommends motoring starts for all starts on the ground for both A and B models. You can’t turn the ignition on before condition lever to start for a motoring start, because not only is the aircraft not designed to do that, it damages the start relay in the PDU.

But what would SAAB know :ugh:

Funny that the engineers do direct starts all the time and the US pilots that transferred to Australia, and the Swedes did direct starts, hey, but what would I know.


Oops what start method is that???

The issue with PDU frying is when selecting fuel and IGN too close together, especially IGN immediately prior to fuel, this has nothing to do with motoring vs direct, its only an issue during motoring starts. It is mainly because it is designed for direct starts, but a motoring start is preferred in any turbine to increase airflow prior to combustion. The start sequence requires both fuel in start and IGN auto to engage properly, if you switch it all on during motoring at the same time the system takes a second or two to recognise where its at and continue, a bit like mashing the keyboard on an old computer. Watching some of the euro operators new procedures actually seems to go against this advice and has the FO putting in fuel at the same time as the captain selecting IGN, seems way overly complicated and runs against the advice leveled. At least the Aussie procedure has the Captain doing all the start so its a clear order.

PS apart from PDU issues of spiking power from an abridged stuffed up motoring start the other downside to motoring are increased wear on everything else not the hot section, starter motor, battery, even just the increased time at load across the electrical system, longer load on the GPU if used, etc etc... Direct starts is designed to get the engine up and running as efficiently as possible, not necessarily the absolute best heat wise across the hot section.

Yes, the engineers sometimes do direct starts. I don’t know, but I’m assuming that during maintenance a direct start must be periodically demonstrated/tested as it’s the inflight restart method.

But it doesn’t change the fact that motoring starts are done by pilots for every ground start because it’s what the manufacturer/AOM recommends.

Not because of A model hangovers, not because of Austronauts, not because of any other reason you tried to explain. And the condition lever is moved to start before ignition for a motoring start BY DESIGN.

You know, you could have just said “I didn’t know that.” or “Oh, that’s why they do motoring starts.”

But good to see you’ve doubled down :ok: Always a good trait as a pilot.

Not doubling down, just on advice from the engineers that direct starts have no real issues, especially on the B model. It measures all the temps etc and manages the start appropriately. The advice is almost universal for all turbines that motoring starts are a little better for the hot sections as you are increasing air flow through the whole system for longer. As for cold starts especially on batteries the direct start may be the only way you are going anywhere if you are not careful with power management. I do find it funny that most Aussie pilots are ****e scared of direct starts when its designed for it. I suppose at least with motoring starts you are watching the sequence more vigilantly so there is that.

From what the engineers say its their standard start method.

BTW I do think it was the A model issue had too rich fuel mixtures on occasion where the direct start had fuel input, uneven combustion, and led to some torching. The motoring leans out the mixture so better combustion at the point of ignition, smoother flow of gases, no torching if its done properly. The A model fuel injectors were also modified for a few reasons, one was inflight relight characteristics and so on, so its probably not as much an issue now either. The B model does not have this issue at all as far as I'm aware so it is a hangover procedure that remained in the AOM as far as I'm aware.

Is it an emergency that fits that requirement of aircraft or occupant safety being threatened?

As was shown, the aircraft flew quite capably from Adelaide to Essendon.

Not until the aircraft touches down does the safety concern/threat arise so, until that touchdown happens, there is no emergency. An abnormal situation, certainly, but not an emergency.