Reports of A400 Crash, Saville, Spain

[KenV]

I hope there's no chance that any element of this software is installed on the ECUs of Airbus civil types . .

Two points:

1. There is zero evidence that the fuel trim software being blamed for this accident resided in the ECU. Usually, fuel system management is handled at the aircraft system level, not at the engine level, so it would seem unlikely this function resided in the ECU.

2. Even if the fuel trim function resides in the ECU, the A400 uses an engine used by no other aircraft, civil or military. So it would seem extremely unlikely that other types of aircraft would be affected.

[KenV]

"If the aircraft had been higher, the outcome may have been different."

A statement that is applicable to practically every aircraft that has ever crashed.

Really? I'm quite sure there have been LOTS of aircraft accidents that would have been totally unaffected by altitude.

[KenV]

Thanks for that Wolf, I was recently discussing this A-400 incident with a current HH-60 pilot and he said the same thing- they were comforted to know that they could mash the levers forward and bypass the electronics/FADEC if need be- a mechanical bypass. Likely part of the legacy inherited from the original post-Vietnam battlefield helicopter requirements.

There is some confusion of terms here.

A FADEC is exactly that: "Full Authority Digital Engine Control". Fuel to the engine is entirely metered/controlled by a digital computer. This function resides in an electronic box often called an ECU, which often has many other functions besides metering/controlling fuel flow. The pilot controls thrust by providing an electronic input to the ECU, which then varies the fuel flow to deliver the thrust demanded by the pilot.

The T700 engine does not have a FADEC. It uses a hydromechanical fuel control system (HMU). The HMU uses many mechanical and analog inputs to meter/control the amount of fuel going into the engine. One of the inputs to the HMU is an electronic unit which provides much finer fuel control and also adds many protections and other features. The PCL can be used to lockout the electronic inputs to the HMU, but the PCL does NOT give the pilot control of engine fuel flow. It only gives the pilots the ability to eliminate the electronic inputs to the HMU. The PCL is NOT a "mechanical bypass" to give the pilot mechanical control of engine fuel flow.

Keep in mind that helo engines are designed to maintain 100% RPM at all times. In a helo the pilot does not change thrust by changing RPM. He changes thrust by changing collective on the rotor system. So the pilot NEVER controls throttle/fuel flow to the engine. He can only control (via the collective) the load put into the engine/drive system and the HMU then controls fuel flow to maintain RPM. There is no link (either mechanical or electrical) between the pilot and the HMU for him to directly control engine fuel flow.

[John Farley]

Keep in mind that helo engines are designed to maintain 100% RPM at all times. In a helo the pilot does not change thrust by changing RPM. He changes thrust by changing collective on the rotor system

That is so right.

However

So the pilot NEVER controls throttle/fuel flow to the engine.

I cannot agree with that. With all for helicopters I flew in the 60s I had to control the RPM at around max by using a twist grip throttle in the end of the collective. As the years have gone by pilots have been assisted in this difficult task (initially) by suitable mechanical links that adjusted the throttle (roughly) as the collective was moved and latterly by FBW systems which of course free the pilot of the task. How many of the older types are still in operation I do not know, but I am sure there are some.

I mention this just so that tryos do not get confused into thinking the helo world has always been like it is today.

[H Peacock]

So the pilot NEVER controls throttle/fuel flow to the engine.

Not always so on modern helos either. Many have a system where a collective input does directly modify the fuel flow in order to anticipate the inevitable small change in rotor RPM that will inevitably follow. Why wait for a large increase in collective to cause a subsequent drop in rotor RPM due to the increased load when it can be anticipated directly?

Thread creep I know, but there really is too much aggression/sarcasm on the pages of contributions to this thread.

Tragic as this accident was, I don't see why this particular fatal accident is worthy of any special consideration over other fatal aviation accidents discussed here on PPRuNe. Am I missing something here??

[KenV]

I cannot agree with that. With all for helicopters I flew in the 60s I had to control the RPM at around max by using a twist grip throttle in the end of the collective. As the years have gone by pilots have been assisted in this difficult task (initially) by suitable mechanical links that adjusted the throttle (roughly) as the collective was moved and latterly by FBW systems which of course free the pilot of the task. How many of the older types are still in operation I do not know, but I am sure there are some.

You are of course correct. I was addressing the H-60 / S-70 family specifically. I even mentioned the twist grip throttle control in my earlier post (#146)

[KenV]

Not always so on modern helos either. Many have a system where a collective input does directly modify the fuel flow in order to anticipate the inevitable small change in rotor RPM that will inevitably follow.

This system is just one more input to the HMU/ECU. The HMU/ECU still controls the fuel flow, not the pilot.

[Tourist]

Plus of course many helicopters such as the seaking still have a manual throttle option if the automated system is acting up where you do in fact control the fuel flow.

[BEagle]

Am I missing something here??

Probably.

Notwithstanding the parallel discussion concerning helicopters, the only salient points we currently have about the A400M accident are:

1. The aircraft suffered a fatal accident.
2. Media reports hint at unofficial industry sources which allude to the loss of thrust from 3 or more engines at low level during the intial climb.
3. The reason for this rumoured loss of thrust has yet to be officially identified.
4. FDR and CVR analysis is ongoing.

As for this specific thread, there has been a clear policy of dissuading every fruitcake and MSFS-geek from the level of wild speculation which so often contaminates the Rumours and News forum.

But I think it's fairly safe to assume that no extraterrestrials were involved......

[KenV]

1. The aircraft suffered a fatal accident.
2. Media reports hint at unofficial industry sources which allude to the loss of thrust from 3 or more engines at low level during the intial climb.
3. The reason for this rumoured loss of thrust has yet to be officially identified.
4. FDR and CVR analysis is ongoing.

Excellent summary. I would add the following:

3. The reason for this rumoured loss of thrust has yet to be officially identified, but the same rumor sources claim it was due to a fuel tank trimming system unique to this specific aircraft and not previous installed on A400s.

It is this last item that started the discussion on FADEC and ECUs, which are likely not involved in a fuel tank trimming system anyway.

[Courtney Mil]

BEags, very well said. I stand by you on this one.

The vultures and armchair experts always turn up at such times.

Originally Posted by H Peacock

Tragic as this accident was, I don't see why this particular fatal accident is worthy of any special consideration over other fatal aviation accidents discussed here on PPRuNe. Am I missing something here??

I doubt you are. I think the groundswell of opinion against the folk that turn up here every time there's an accident to post ludicrous speculations (for God alone knows what reasons) has done nothing other than piss us all off for a long time. Maybe it took a single request from a single poster to prompt us all to try to put a stop to the rubber-necking.

Not "special consideration". The consideration we should give to all such incidents.

Edit: sorry, HPeacock, I did not mean to imply that you are one of those that come here to speculate. I was addressing two issues in one post and failed to separate the two.

[BV234driver]

Tank trimming?

What is the benefit of tank trimming, and how would this expand the maneuver envelope at takeoff versus any other normal mode of flight? Have read several of the articles, but drawing a big question mark on this one.

Resorting back to fixed wing aero, you'd like the Cg to be near CL as I recall- thus alleviating any control or flying qualities issues... It appears I need a class in how this functions as a benefit- other than doing exactly the above...which I'd assume in a production aircraft you'd thus be at a full or ideal load anyway, and not likely require shifting at takeoff?

[Brian W May]

I've been wondering why an aircraft would need tactical manoeuvering immediately after take off, then thought about MANPAD etc, so presumably that's why.

What I don't understand is - when an aircraft this large manoeuvers, are they not likely to be positive g rather than negative? So I am at a loss to work out what fuel tank trimming actually means in this context.

Does this cause trimming of thrust to assist the aerodynamics? Care to enlighten me anyone?

[ORAC]

AW&ST: A400M Countries Form Monitoring Team, Germany Warns Of Airlift Gap

[SyEng]

Fuel Trim

Unlike some Airbus types, the A400M does not feature "fuel tank trimming". There is no trim tank in the tail. Neither is fuel pumped laterally (except, if required, under manual pilot control to correct a fuel imbalance). The fuel's path from tank to engine is untroubled by any software. The Wikipedia and Aviation Week articles are a load of bull.

[Brian W May]

Thanks - so it's "simply" a means of altering C of G. For some reason I thought it meant lateral trimming - which blew my mind.

[SyEng]

Brian, no, there is no fuel CG trimming on A400M: neither longitudinal nor lateral. Apologies if my previous post was unclear.

[charliegolf]

Am I safe to ask: is there any news (good, preferrably) on the recovery of the survivors yet?

CG

[BEagle]

SyEng, have any A400M been flown with the additional Cargo Bay Tanks intended for the AAR role? Fuel from the CBTs will need to be pumped to the 'AAR gallery', although I cannot recall how the associated schedule is managed.

If 'AAR' software is enabled and the fuel system is 'expecting' to transfer fuel from CBTs which aren't actually fitted.......

And no, I have absolutely no idea whether the AAR software has yet been included in any A400M.

[Trumpet_trousers]

CG:
Both still recovering in hospital, the most seriously injured guy is, thankfully, out of intensive care.
Beagle: No, the CBTs and the centreline HDU stuff is yet to be trialled.

My understanding of the Tactical fuel management is that it schedules the fuel in such a way that it minimises stress/fatigue due to the more dynamic manoeuvring required for the tactical role, up to +3G.