Hot & hung start criteria in CF6 autostart program

[Hardy Heinlin]

Good morning,

the autostart programs in the current PSX versions are based on engineering documents. These seem to disagree with the autostart programs in some other certified simulators.

I've been asked to make the PSX autostarts (for CF6) behave like those in the other certified sims.

Now I'm not sure whether I should make this modification optional or fixed. I don't know whether the engineering data is inaccurate or the other sims are inaccurate -- or both. (I learned that some certified sims are more or less simplified in terms of autostart simulation.)

For example:

Documents say: 2 minute motoring after last attempt, then display AUTOSTART message
Other sims do: After last attempt immediately display AUTOSTART message and start 30 second motoring

Documents say: Hot start is EGT >960
Other sims do: Hot start detection before EGT >750/960 **

Documents say: Hung start (stall) is N2 rate of change <15 rpm/sec for 15 sec, and EGT >750
Other sims do: Hung start detection before EGT >750/960 **

** It could be that the other sims do use the documented limits, but the EGT tape and box just won't turn red during this short-term exceedance?

Any opinions?


Regards,

|-|ardy

[Will]

It sounds like you're considering making a simulator simulator!

I totally understand why a customer might want PSX to simulate a certain simulator, and you could do it with a radio button somewhere that says:

(0) Autostart logic as per ____ simulator

... but would it be logical to stop there? I mean, there are probably several ways that simulators differ from aircraft... and simulators might even differ from each other, so it would be hard to cover all the bases, I imagine.

On a related note, I once day-dreamed of a package with two components, a simulator simulator and an aircraft simulator. The simulator simulator would do everything that simulators do, while the aircraft simulator would not allow repositioning, would not allow pausing or motion-stop, would no allow in-flight fixing of broken systems, would use only real-world weather, and would allow only one "instance" of a particular aircraft. Hours and events would be logged, and if it suffered fatal damage, then it could never be flown again. So people could train in the simulator simulator environment, and then "compete" in the aircraft simulator environment, to see how many hours one could accumulate without a hard landing, or how many challenging airports one has visited without incident, and so on.

[Hardy Heinlin]

So would you buy another "aircraft simulator" when your current one destroyed itself? :-)

As for the last 30 second motoring and the message trigger before that: I just learned that this is mentioned in the AOM of another airline. So it's not wrong, but maybe just airline or version specific.

I think I'll make the modification fixed, not optional.


Cheers,

|-|ardy

[Will]

No, you could create as many aircraft as you want, but each one that was created would only have one life.

[Skybird]

According to maintenance manual and simulator briefing:

For HOT start >750 / HUNG start (Lack of N2 acceleration) or Compressor stall (EGT too high for given N2):

                         3 start attempts with motoring (in between) and 2 reduced fuel schedules (cumulative)
                         The 2 first motoring = 6 sec. The last one = 2min.
                         Autostart message comes at the end of last motoring

The maintenance document is supposed to reflect the reality. Unfortunately, I don't have any precise value for the Hung start.
The maximum EGT on ground is 870 (40 sec above 750). Tapes become red at the red index (750).

The 960 is the maximum EGT start value in flight. If I remember well, the indication, however, becomes red passing 750, but the autostart system will retain the 960

[Hardy Heinlin]

This agrees with the data I have. But it disagrees with another AOM and some sims.

Do you know how old your source is?

The maximum EGT on ground is 870 (40 sec above 750). Tapes become red at the red index (750).

This is confusing. So, on the ground, is it 870 or 750? And if there's a 40 sec delay, will the tape really turn red immediately or only after 40 sec? The latter would explain why the other sims don't turn red before autostart reacts.

[Skybird]

Crew are not supposed to know this 870 limit.

So the tape becomes red as soon as passing 750.

The 870 limit is in the AFM - last revision OCT 18. But it's not new, was there for long time.

Sources for the Hot/Hung start: 2003, 2005, 2008, FCOM 2018

[Jeroen Hoppenbrouwers]

Would it be feasible to "just" add options as usual, and then create "tail numbers" like we already do to capture specific simulators, mentioned by make and model, plus airline or sim center?

[Hardy Heinlin]

Would it be feasible to "just" add options as usual, and then create "tail numbers" like we already do to capture specific simulators, mentioned by make and model, plus airline or sim center?

Yes, maybe.

The maximum EGT on ground is 870 (40 sec above 750). Tapes become red at the red index (750).

I still don't understand the link between "870" and "40 sec above 750". What are these 40 sec for?

[John H Watson]

I still don't understand the link between "870" and "40 sec above 750". What are these 40 sec for?

It's like sticking your hand in a flame (at various distances to the hottest part of the flame). How long can you keep it there before it starts to burn you. Exceedances are measured in time x temperature.

Metal components start to degrade/soften when subject to lower temperatures over time.

Hardy: Ref Instru Book 1 page 397 for "exceedance snapshots". We replace engines depending on the time spent at each temperature.

[Hardy Heinlin]

That's clear. But what have these 40 sec got to do with the autostart logic?

[John H Watson]

Our 2016 FCOM says 30 seconds for the final motoring. The text is highlighted showing a change (circa 2016)

GE aircraft:

During ground start, the autostart system monitors engine parameters and aborts
the start for any of the following malfunctions:

Note: The autostart system does not monitor oil pressure or N1 rotation.
Note: The autostart system does not monitor oil pressure.

If the EEC detects no EGT rise, it cuts off fuel and ignition. The engine motors for
30 seconds. The EEC applies fuel and ignition to both igniters for another attempt.
The EEC makes three attempts before aborting the autostart sequence. The engine
motors for 30 seconds before the start and bleed air valves close.

If there is an EGT rise, but the EEC detects an impending hot start or a hung start
before starter cutout, it cuts off fuel, adjusts the fuel schedule, then reapplies fuel
for another attempt. The EEC makes three attempts before aborting the autostart
sequence. Fuel and ignition are cut off. The engine motors for 30 seconds before
the start and bleed air valves close.

If the EEC detects an impending hot start or a hung start after starter cutout, the
autostart sequence is aborted immediately. The engine does not motor.

The AMM is very slow to be modified (if ever).

The manuals I have don't specifically say that the AUTOSTART message appears at the end of the final motoring period. I'm just checking the system schematics for logic diagrams... One of the logic gates for the message includes an input called "ABORT". It could mean that the EEC has initiated the cooldown period after the last failure.

From my training manuals:

If light off does not occur within 15
seconds on the third attempt, ignition and fuel are shut off, the
engine is motored for two (changed?) minutes and the autostart sequence is
aborted. An ENG (1) AUTOSTART advisory message is sent to the
EICAS display.

It doesn't specifically say when the AUTOSTART message appears.

[Skybird]

Hardy, John,

It doesn't specifically say when the AUTOSTART message appears.

The 2 minutes motoring after the 3rd start attempt can be found on the start sequence diagram published by Boeing company chap 80-11-00-p449 of the training AMM published in 2003. This diagram is commented on the p448 with a plain text which says:

If light off does not occur in 15 sec (3rd try), ignition and fuel go off, the engine motors for 2 minutes, and the autostart sequence stops. An ENG AUTOSTART advisory message shows on the EICAS

If you have a doubt regarding the moment the autostart message appears on the EICAS, just imagine what could happen by having the message well before the 2 min are elapsed:
According to Boeing procedures, the crew is trained to execute memory items which are in this precise case, as soon as the message appears, to set the Fuel Control Switch to CUTOFF. By this action, the autostart sequence is interrupted before the end of his full sequence. There will consequently be NO motoring.
So, the autostart message MUST be shown at the end of the 2 minutes.

And by the way, this same diagram has been customized in the Training Maintenance Manuel of a major german airline 


Regarding the >750 Timing 40sec Max 870° - < 750 limitation: up to now, I don't know if this program is part of the autostart or not. It's purely AFM info.

Steve

[Hardy Heinlin]

It makes sense to show the message after the 2-minute dry spin is completed.

But in that last upgrade they did not only change the 2 minutes to 30 seconds, they also put the message before the dry spin.

Well, maybe 30 seconds are short enough, so that the crew will first read the QRH items which may take 15 seconds, and then look at the start and fuel switches and confirm, which may take another 10 seconds ... and then the dry spin will be over anyway :-)

The message itself also incorporates a delay of a couple of seconds.


|-|ardy

[John H Watson]

The 2 minutes motoring after the 3rd start attempt can be found on the start sequence diagram published by Boeing company chap 80-11-00-p449 of the training AMM published in 2003. This diagram is commented on the p448 with a plain text which says:

Quote

    If light off does not occur in 15 sec (3rd try), ignition and fuel go off, the engine motors for 2 minutes, and the autostart sequence stops. An ENG AUTOSTART advisory message shows on the EICAS

Hi, Steve...  Seems like we have the same book. Throughout PSX's long development, we have found dozens of variations between the AMM, wiring schematics, AMM training manuals, Service Bulletins, sims, FCOMs, real aircraft, etc. If we get two or more in agreement, it's a good sign  The training notes have been a good backbone. Unfortunately, they are getting outdated and some have been modified to suit specific companies (by the company) and the variations are not necessarily Boeing-approved and have been found to be wrong. On the other side, PSX development has even resulted in a few emails being sent to Boeing to tell them their manuals/diagrams are wrong!

By this action, the autostart sequence is interrupted before the end of his full sequence. There will consequently be NO motoring.
So, the autostart message MUST be shown at the end of the 2 minutes.

Im not sure I follow your logic. Of course, if the cooldown period did take two minutes without a message, the crew would most definitely intervene prematurely. Perhaps that's why the logic was changed. The QRH procedure for the AUTOSTART message does include the fuel levers to cutoff and a further manual 30 second dry spin period.

There is a vaguely labelled ABORT box in the wiring schematics leading to the AUTOSTART message. Does manual intervention during Autostart generate the AUTOSTART message or is this referring to the EEC aborting the autostart?

Autostart Caution Logic (in EIU)

[Mariano]

Hardy,

Perhaps this can help, last two pages especially.

I skim-read the post and document while walking through an airport, so I might not have fully understood the actual issue, in which case document might be of no use.

https://www.dropbox.com/s/r0gm69mw8h1k9dr/GE%20CF680-C2B1F%20Autostart.pdf?dl=0

Best regards,

Mariano

[Hardy Heinlin]

Thanks, Mariano.

[Hardy Heinlin]

The GE autostart software update is now available in PSX 10.72:

http://aerowinx.com/board/index.php?topic=4191.0


|-|ardy