Posts about: "FADEC" [Posts: 233 Pages: 12]

BrogulT
July 14, 2025, 04:36:00 GMT
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Post: 11921851
Originally Posted by skyrangerpro
The extract below shows that from Idle to 83% N1 took 5 seconds after the initiation of a TOGA, so I think your estimate of 30 seconds is probably too high. However, after reading that report, I am of the opinion that AI 171 had no chance of recovering. If the FCS switches had been set to Run within 5 seconds of being set to Cut Off, there might just have been a chance, but it is not at all certain.
As I understood the question, the issue was what impact the lack of electrical power had on the restart. In this case, without the APU (or the other engine) for power the right engine was apparently never going to start despite heroic efforts on the part of the FADEC. With the APU running it could have been cranked. However, going from flight idle to full thrust is one thing, going from so far below idle that the engine needs to be cranked to flight idle will take a lot more time. How much more IDK since exactly how far the N2 speed had dropped, actual airspeed, temperature, etc are all factors. My guess is that it would feel like the engine was taking a million years to start. But the APU was not running and the point is moot.

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EDML
July 14, 2025, 17:48:00 GMT
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Post: 11922392
Two questions for tdracer :

1. What happens to the FADEC channels if both channels have different data / information (e.g. T/L encoders or fuel switches)?
- Will the currently active channel win?
- Or will the most sensible information be used (e.g. keep the engines running)?
- Will there be a disagree message?
- Logged to the DFDR?

2. As per the data sheet the fuel switches are 4 pole versions. 1 pole will be used for each FADEC channel. Will one (or both) of the other poles be used for the DFDR or is that information collected from the FADEC through some data bus?

I know, it's very specific stuff that might only be known by the designer of the FADEC system.

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tdracer
July 14, 2025, 18:16:00 GMT
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Post: 11922406
Originally Posted by EDML
Two questions for tdracer :

1. What happens to the FADEC channels if both channels have different data / information (e.g. T/L encoders or fuel switches)?
- Will the currently active channel win?
- Or will the most sensible information be used (e.g. keep the engines running)?
- Will there be a disagree message?
- Logged to the DFDR?

2. As per the data sheet the fuel switches are 4 pole versions. 1 pole will be used for each FADEC channel. Will one (or both) of the other poles be used for the DFDR or is that information collected from the FADEC through some data bus?

I know, it's very specific stuff that might only be known by the designer of the FADEC system.
An unresolved difference in TLA between the channels is quite unlikely - the fault detection algorithm is quite good (sine squared plus cosine squared) - but it can happen. In the old days, we'd default to the higher TLA, but since the feds became preoccupied with Uncontrollable High Thrust, we tend to select the lower value. Worst case would be to default to idle. The fuel switch discrete doesn't really get used except for engine start - if it falsely indicates shutdown (on one or both channels), the FADEC won't do anything if the engine is already running. All this will set maintenance faults - and associated EICAS Status messages (L/R ENGINE CONTROL or ENGINE C1). I doubt that would be recorded on the DFDR - it would go to the QAR but that's unlikely to survive a crash. It would also be logged in the FADEC NVM - but again no guarantee that would survive either (although when the Lauda 767 crashed due to the thrust reverser deployment, the DFDR was destroyed but the FADEC NVMs both survived - much of what we know about that crash came from the FADEC NVM.)

Again, not familiar with the specifics of the 787, but on the 747-400/-8, one pole of the fuel switch feeds EICAS - which uses it in various message logic - and sends it out to any other aircraft systems that use it. There is "Digital Flight Data Acquisition Unit) DFDAU (pronounced Daff Du) that takes all the various system digital signals, sorts them and provides them to the DFDR and QAR. The 787 has something similar to the DFDAU but I don't recall what it's called.

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EDML
July 14, 2025, 18:50:00 GMT
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Post: 11922425
Originally Posted by tdracer
... The fuel switch discrete doesn't really get used except for engine start - if it falsely indicates shutdown (on one or both channels), the FADEC won't do anything if the engine is already running. All this will set maintenance faults - and associated EICAS Status messages (L/R ENGINE CONTROL or ENGINE C1)...
Sorry if my wording was not precise here - I meant the fuel cut off switches that more or less caused this accident.

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GroundedSpanner
July 14, 2025, 21:09:00 GMT
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Post: 11922503
Originally Posted by tdracer
Again, not familiar with the specifics of the 787, but on the 747-400/-8, one pole of the fuel switch feeds EICAS - which uses it in various message logic - and sends it out to any other aircraft systems that use it. There is "Digital Flight Data Acquisition Unit) DFDAU .... that takes all the various system digital signals, sorts them and provides them to the DFDR and QAR. The 787 has something similar to the DFDAU but I don't recall what it's called.
787 has RDC's - Remote Data Concentrators. Doing the same function. Two of the switch pole-sets go each to one of 2 different RDC's, that feed the EAFR's / QAR, and the common core network so that any system that wants to know, can. The wiring is positive voltage from the RDC's to the switch and to GND through the common pin. So the RDC's would be able to detect anomalies such as both contacts open, or both contacts closed. The EAFR will see two independent channels per switch.
The other 2 contact sets feed latching relays (again driven each coil independently by dropping to GND at the switch) that then drive spar valves and reset signals to the FADEC Channels. (and more).

So - for the benefit of those that hang on to the 'possibility' of electrical gremlins and 'ghost' switch signals.

Each switch has 4 mechanically separated 'channels' - 2 of which do electromechanical things to the engines through separate paths, the other 2 feed through independent paths the FDR and the rest of the computer systems. The results of the electromechanical actions also feed back to the FDR.

Thus the readout from the EAFR will PROVE that the switches MUST have been PHYSICALLY MOVED.

And - I'm nervous to challenge you tdracer - there's quite the authority gradient and I know I'm at the bottom end, but I can't let this fly...
Originally Posted by tdracer
DFDAU (pronounced Daff Du)
Its 'Deefer Doo'. Fight me.

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JustusW
July 15, 2025, 10:26:00 GMT
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Post: 11922807
Originally Posted by clearedtocross
Lets assume the perliminary report contains facts and lets give the pilots the benefit of doubt. What electrical/electronic failure could produce the simultaneous shut down of both engines?
This has been discussed to death previously. I suggest looking for tdracer's excellent insights into FADEC design and implementation. From the beginning we've been discussing various very rare types of circumstances. Based on the preliminary report we can now lay most of those to rest.

Originally Posted by tdracer
The fuel switch discrete doesn't really get used except for engine start - if it falsely indicates shutdown (on one or both channels), the FADEC won't do anything if the engine is already running. All this will set maintenance faults - and associated EICAS Status messages (L/R ENGINE CONTROL or ENGINE C1). I doubt that would be recorded on the DFDR - it would go to the QAR but that's unlikely to survive a crash. It would also be logged in the FADEC NVM - but again no guarantee that would survive either (although when the Lauda 767 crashed due to the thrust reverser deployment, the DFDR was destroyed but the FADEC NVMs both survived - much of what we know about that crash came from the FADEC NVM.)

Again, not familiar with the specifics of the 787, but on the 747-400/-8, one pole of the fuel switch feeds EICAS - which uses it in various message logic - and sends it out to any other aircraft systems that use it. There is "Digital Flight Data Acquisition Unit) DFDAU (pronounced Daff Du) that takes all the various system digital signals, sorts them and provides them to the DFDR and QAR. The 787 has something similar to the DFDAU but I don't recall what it's called.
Which actually brings me to this one because I would like to ask for a bit of clarification: By "fuel switch discrete" are you referring to the Fuel Control Switches discussed in the preliminary report?
I would assume from your statement, that if a mismatch in the NC/NO signal on the switch was detected the FADEC would not direct the Fuel Cutoff Valves to close (as far as the types you are familiar with are concerned), is that correct?

The report states:
[...] at about 08:08:42 UTC [...] the Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position one after another with a time gap of 01 sec. The Engine N1 and N2 began to decrease from their take-off values as the fuel supply to the engines was cut off.
So this would then mostly preclude the possibility of one or both switches being faulty electrically.

The report then states:
As per the EAFR, the Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN at about 08:08:52 UTC. [...] Thereafter at 08:08:56 UTC the Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN.
There is a 10 second gap between cutting fuel and re-enabling it and a 4 second gap between switches during re-enabling. Is there a mechanical reason why these switches would be slower to operate in either direction? There are obviously reasons such as startle factor and stress that might negatively affect the speedy operation of switches by anyone, but I am nonetheless curious if this might not be a pointer to some sort of mechanical issue after all, such as asymmetric wear or FOD.

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EDML
July 15, 2025, 14:00:00 GMT
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Post: 11922968
Originally Posted by JustusW
...
Which actually brings me to this one because I would like to ask for a bit of clarification: By "fuel switch discrete" are you referring to the Fuel Control Switches discussed in the preliminary report?
I would assume from your statement, that if a mismatch in the NC/NO signal on the switch was detected the FADEC would not direct the Fuel Cutoff Valves to close (as far as the types you are familiar with are concerned), is that correct?
...
I first didn't understand his answer as well (it was my question). In the meantime I know more about the logic: The fuel shutoff valves are not operated by the FADEC. The switches are wired directly to latching relays that drive the (latching) fuel valves. Using an additional pole of that switch the FADEC just gets the information that the switch was operated (and of course the current position). The FADEC can then e.g. execute the engine restart sequence if required.

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LiveSpark
July 16, 2025, 21:26:00 GMT
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Post: 11924011
Originally Posted by GroundedSpanner
787 has RDC's - Remote Data Concentrators. Doing the same function. Two of the switch pole-sets go each to one of 2 different RDC's, that feed the EAFR's / QAR, and the common core network so that any system that wants to know, can. The wiring is positive voltage from the RDC's to the switch and to GND through the common pin. So the RDC's would be able to detect anomalies such as both contacts open, or both contacts closed. The EAFR will see two independent channels per switch.
The other 2 contact sets feed latching relays (again driven each coil independently by dropping to GND at the switch) that then drive spar valves and reset signals to the FADEC Channels. (and more).

So - for the benefit of those that hang on to the 'possibility' of electrical gremlins and 'ghost' switch signals.

Each switch has 4 mechanically separated 'channels' - 2 of which do electromechanical things to the engines through separate paths, the other 2 feed through independent paths the FDR and the rest of the computer systems. The results of the electromechanical actions also feed back to the FDR.

Thus the readout from the EAFR will PROVE that the switches MUST have been PHYSICALLY MOVED.
Can someone please confirm whether or not the respective fuel cut-off switch is directly connected to the open/closing coils of the fuel valve actuator? Or is there some intermediate control system between the switch and valve actuator?

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tdracer
July 17, 2025, 04:18:00 GMT
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Post: 11924121
Originally Posted by EDML
Two more questions for tdracer ;-)

Are the FADECs able to drive the fuel shutoff valves as well? I would guess that this might be used for N2 overspeed protection (and therefore TCMA as well). If there is an overspeed there would be a good chance, that the fuel control/metering doesn't work as it should.

I am not asking to revive the switch discussion - I am just curious.

And one more question: Are the fuel shutoff valves powered by the PMG for the FADECs? I know the valves are latching so that a power failure of any kind wouldn't change their position.
The answer is slightly complicated. The FADEC has the authority to move the fuel metering valve to the 'full closed' position - which also causes the High Pressure SOV to then close. However this is normally only used during engine starting, and that part of the logic is disabled once the engine is running. However, there is the overspeed protection circuit which can also close the HPSOV. TCMA uses the overspeed protection system to shutdown the engine.

The HPSOV is driven by the aircraft using 28 Vdc power from the battery bus. The FADEC isn't involved - although it does get an indication of the fuel condition switch position, but that's not used except during starting. A 'false' fuel condition switch input of Cutoff will not cause the FADEC to do anything once the engine is running.

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tdracer
July 17, 2025, 07:46:00 GMT
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Post: 11924194
Originally Posted by Lead Balloon
I'm confident I'm far from alone. I do take objection to the connotations of your suggestion that my motivation is to "just to satisfy [my] curiosity". If you read what I wrote, my motivation has nothing to do with anything as trivial as satisfying my curiosity. But I'm assuming you meant no offence.

However, the 'bottom line' is that you're almost certainly correct and this investigation will carry on for however long the investigators choose to take, while choosing to reveal or withhold whatever they chose to reveal or withhold, and ICAO will continue to do the things that bureaucracies tend to do. In the meantime, the thousands of family members and friends of the deceased will be at the mercy of speculation and leaks of unknown origin.

There are good, valid reasons for the ICAO accident investigation rules - and one of those rules says they'd don't release information until it is properly vetted and validated. As I posted previously, the preliminary report actually had more data that most - it would have been very easy for them to have simply said that the engines quit - one second apart - starting 3 seconds after liftoff. Instead they added detail, including a brief synopsis of a pilot conversation regarding the fuel switches. All this is factual. What they don't release is non vetted information and speculation - such as who moved the switches and why - because that's still being investigated.
Early releases of unvetted data can not only cause unproductive public reactions, it can result in external pressures being applied to the investigative team that can adversely affect their ability to come to the correct cause. Furthermore, I cannot recall a single preliminary report that contained anything like an actual CVR transcript. Those are routinely included in the final report, but not preliminary reports. About the only time you'll see unvalidated information is when there is a suggestion that there is an imminent air safety threat - in which case appropriate emergency inspections are ordered (sometimes even aircraft groundings).

I have a pretty vivid memory: In the aftermath of the Chicago DC-10 crash when the engine ripped off the wing, a couple of days later some department head (I don't remember if he was FAA or NTSB) stood on the podium holding a broken bolt and pronounced that it was the reason the engine came off. Unvetted information that turned out to be complete BS - but resulted in massive outrage that 'the engine was held on by one bolt' - more BS. Fortunately it didn't derail the investigation - and even had a silver lining in that the order bolt inspections lead to the discovery of the actual pylon structural damage that had caused the engine mount to fail. Similarly, after the Columbia Space Shuttle disaster - I watched the clueless head of NASA stand in from of the TV cameras and state as fact that a piece of foam could never have punched a hole in the Columbia wing (obviously never studied that mass*velocity squared thing) - which of course we again know was complete BS.

I've been involved in a few fatal accident investigations - the big one being the Lauda 767, where I was called in early. I was one of the first people to see the FADEC NVM readout that made it painfully obvious that the T/R had deployed at 23,000 ft. - something that we didn't think could happen. We (Boeing) had missed something, and a lot of people had died as a result. It really bothered me (more than once during that investigation, when I got home from work, I just sat down and drank a large glass of Scotch). And not being able to discuss any of it with anyone not involved in the investigation just made it worse. But I knew the rules, understood why there where there, and I followed them.

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AdamB28
July 17, 2025, 13:29:00 GMT
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Post: 11924405
Originally Posted by OhForSure
I have not posted on here in many years, but I feel compelled to do so now. I am a current 787 pilot and I have previously flown most Boeing types and an Airbus too. I also have an extensive background and qualifications in human factors, training and assessment. Before anybody reads any further, perhaps acquaint yourself with the notion of Occam's razor. That is, the simplest explanation is the most likely explanation. I was certain that after the preliminary report was released the preposterous conspiracy theories would finally cease, but no! It's 2025 and humans can no longer help themselves. In my opinion the captain committed suicide here. Simple.

To those suggesting an electrical phantom turned the fuel control switches off without them moving: no. Ask yourselves this: what made one pilot (PF and F/O in my opinion) ask the other "why did you cut off?" Firstly, some context. The 787 fuel control switches make a VERY distinct metallic *CLICK* sound as they are operated. EVERY 787 pilot knows it and won't forget it. It is audible even at high thrust settings owing to the 787's exceptionally quiet engines and cockpit. After rotation the pilot flying is fixated on the HUD; rotating towards the TOGA reference line (~12 degrees pitch attitude) and putting the flight path vector over the flight guidance cue. One hand would be on the control column and the other on the thrust levers. Alternatively he could have had both hands on the control column. In either scenario, the pilot flying's (again, my opinion the F/O's) inboard arm would block his peripheral view (he's focused on the HUD, remember) of the center pedestal and the fuel control switches. HE WOULD NOT SEE THE PM TURN THE FUEL CONTROL SWITCHES OFF. Ipso facto. We know the F/O was PF from the report. If the F/O stopped flying the aircraft and reached down to move the FCS from cutoff to run the captain would've plainly seen the whole thing. I can't imagine "why did you cutoff?" would be his words of choice! More like "WTF ARE YOU DOING?!?" More to the point, if the PF (F/O) did stop flying and reach down to cut one engine off, the captain would have had time to either stop him flicking the second FCS off or at least quickly flick them both back to run and potentially save the day. This plainly did not happen. So it was almost certainly the PM (Capt) that moved the fuel control switches.

So what would make the PF ask the PM "why did you cut off?" if he couldn't see it happen? You would never assume with a loss of thrust that the switches had been turned off. Never. It's not a procedure. It's not a thing. Bird strike? Sure. Fuel Contam? Maybe. But the point is, in the heat of battle at 150 odd feet, you'd never jump to the conclusion that the fuel control switches were off. Never. So what triggered the PF asking the PM why he cutoff? Because he HEARD the fuel control switches move from run to cutoff, that is why. He heard those distinctive *CLICK* sounds (and yes, you can easily flick them both in less than a second FWIW) followed by the engines immediately rolling back. He would then have looked down at the switches and noticed they were in cutoff. The point to be made here is that the switches were moved by the captain. They made their distinct sound. There were no phantoms. They cannot move on their own. They didn't simultaneously fail. This drew the PF's attention away from flying and triggered the question "why did you cutoff"?

Inadvertent selection of the wrong switches? No. The PM was a training captain with thousands of hours experience on the jet. I asked one of our most experienced examiners how many times he'd seen that done. The answer was "zero". Even the stab switches next to them. They're red, guarded and are of a completely different shape and operation. Gear or flap? Come on. I think we're starting to stretch things a bit now. EVEN IF it was inadvertent switching. The INSTANT you'd made that error, you'd go "oh whoops", and flick them back to run. I know startle... I teach it. This is different. You don't flick the fuel control switches off, hear the engines roll back and sit there wondering what happened for 10 seconds AFTER THE F/O JUST ASKED YOU IF YOU CUTOFF! You did something that had an instant effect on the flight. The report indicates that "why did you cutoff" was asked just after both engines rolled back. But it took another 10 seconds to flick the FCS' back to run. If it was inadvertent, the instant the other pilot called out your error you'd correct it. The report makes it clear that there was 10 seconds between that happening. 10 seconds is a LIFETIME in that situation. The training captain knew what he was doing. He only switched the FCS' back to run once he knew it was moot.

So, why did he respond that he didn't move the switches? As per other input from people on here, when people are suicidal they often want to throw authorities off their trail. Or maybe he wanted to confuse the F/O so he didn't flick them back to run himself, or to just buy himself more time while the F/O tried to wrap his head around things? Maybe he didn't want the F/O to die knowing it was a suicide mission. Maybe we'll find out more in the final report or police investigation if things proceed that way. Maybe we'll never know.

I acknowledge that this is my opinion and of course there could be things we don't yet know about, but I must say I'm surprised that some of the theories on this professional pilot forum are no more coherent or logical than those being sprouted on social media.
52 pages and finally we get to the money shot.

For those asking why not wait a bit longer before throwing the switches and hard nose down, why bother? Roll them back here, cause a startle that is JUST long enough and then let gravity and the FADEC start a race. No resistance needed.

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T28B
July 25, 2025, 14:53:00 GMT
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Post: 11928262
https://aviationweek.com/air-transpo...N1000041876164
From the article by Guy Norris of Aviation Week... Air India 787 Crash Being Investigated As ‘Criminal Act,’ Says Safety Expert
Guy Norris July 23, 2025

LAS VEGAS—India’s Aircraft Accident Investigation Bureau (AAIB) is now looking into the June 12 crash of an Air India Boeing 787-8 as an intentional act, says veteran safety consultant and former NTSB investigator Greg Feith . The AAIB’s preliminary report on July 12 revealed that fuel cutoff switches for the 787’s two GE Aerospace GEnx-1B engines were transitioned from “run” to “cutoff” around three seconds after takeoff from Ahmedabad Airport. Although both fuel switches were turned back on within a further 14 sec., the aircraft was too low to recover and impacted trees and buildings, killing 241 of 242 occupants on the 787 and 19 on the ground.The AAIB has criticized subsequent western media reports as “irresponsible” for indicating the fuel cutoff switches were likely deliberately moved by one of the pilots.
However, Feith says: “It has become very apparent, especially now with information I know and what's come out about the cockpit voice recorder—where the question is heard ‘why did you cut off the fuel?’—[that] somebody had to have seen that action to make that statement. You just wouldn’t have a dual-engine failure.”

Speaking at the American Institute of Aeronautics and Astronautics Aviation forum here in Las Vegas, Feith says: “Something had to prompt that type of comment. Now we get into the psychology part of it, and that's really where this investigation is going to go. “And oh, by the way, it's no longer an accident. It's investigated as a criminal event, just like EgyptAir, just like Germanwings, just like SilkAir. These are criminal events—intentional acts,” he adds, referring to three fatal crashes deemed to have been deliberately caused which occurred in 1999, 2015 and 1997 respectively.

Feith, who participated in the investigation into the SilkAir crash—where a Boeing 737-300 traveling from Jakarta to Singapore was downed—says other theories continue to persist in the face of contradictory evidence provided by the AAIB. “To this day, people are still talking about this as a dual-engine failure, despite the fact that the AAIB came out with a preliminary report which gave some initial findings. They said at this stage of the investigation, there are no recommended actions for the 787-8 or the engines. They just exonerated the airplane. They just exonerated the engines.”

“The junior investigators and the trolls are still making a big deal about engine failure, software issues, FADEC problems. They're not part of the process,” Feith continues. The AAIB “had a team of subject matter experts dissecting all of this in that 30-day period. You think they didn't look at that? It makes no logical sense,” he adds.

“The fact is that now we have people all spooled up looking at the wrong thing instead of looking at, 'is this an isolated problem or a systemic event?' It's the first major accident for a brand-new airplane [type]. This is the kind of controversy that gets stirred up and distracts us from really looking at where we need to be and what we need to be doing to enhance aviation safety,” Feith says.

Referencing the SilkAir accident, he says: “I've been down this road. I spent two years working on SilkAir in Palembang, Sumatra. I took a team of investigators over with me from Boeing and the engine manufacturer, the FAA and a variety of others, and we determined in concert with their National Transportation Safety Committee, that this was an intentional act.”
If / when we get confirmation that India is indeed going ahead with a criminal investigation, we'll re open this thread.

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tdracer
August 06, 2025, 19:01:00 GMT
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Post: 11934341
Originally Posted by fdr
T
I do a fair amount of flight testing, and that involves some odd activity, and I don't trust myself to not make slips or errors, to the extent that for one aircraft, I carry a tennis ball that fits neatly over the end of the emergency shutdown handle of the engines that I am not intending to shutdown and subsequetly relight.
Having gone on countless flight tests during my career, I was always impressed by the competence and abilities of the Boeing Flight Test Pilots. Most of the flight tests I participated in involved at least one engine shutdown and windmill relight (part of our standard 'First of Model' FADEC software cert flight). The pilots would always use extreme care to make sure they got the correct engine - including putting their hand on the fuel switch and having the other pilot confirm it was the correct switch before setting it to CUTOFF.

But even Flight Test pilots can have a brain fart. Didn't happen to me, but it did happen to one of my best friends. They were doing in-flight start testing of the 757/RB211-535 (and the Rolls engine is a bit notorious for being a fickle in-flight starter). They were doing a corner point condition when the test engine went into a hot start. One of the observers said something like 'it's gone hot, shut it down'. The left seat pilot calmly reached down and shutdown the good engine . Fortunately they were at about 30k, and they were able to recover and get both engines restarted before losing to much altitude.

I was told the Flight Test pilot in question was immediately demoted from "Experimental Flight Test" to "Production Flight Test" (where they do routine shakedown flights of new production aircraft prior to delivery).





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