Air Zimbabwe 767 Engine Surge, Tailpipe Flames, Mayday... Continues to Destination

[3WE]

I parked next to [a J-31] a couple times.

Whenever I could watch the start up, the temperature marched a good bit past a red line (20 to 30%) and then when the engine really kicked in, it rapidly dropped to maybe 80% of the red line.

The pilots never flinched/responded did anything, so I ass-umed that getting 'hot' for a short time was a normal part of startup- and it would make sense that the red line in flight would be "something is not working right" and not_necessarily "something is melting".

Now, to complicate things- an ag pilot friend (who should know a little bit about starting PT-6 engines), stated that his goofball pilots hot started both engines the one time he puddle jumped to Flyover...then again, the ag pilots I know are just a little bit cowboy improvisational...

Then again-again, I should probably check the Internet for what engines are on a J-31 and an AT-802...and their type-specific starting procedure...I believe that most AT-802s are powered by second hand turboprop airliner engines, too.

[ATLcrew]

But you have a digital temp readout as well, so you have an absolute value, right? (BTW, I'm NOT asking about hot start, that was just the precedent I based this on. I'm asking about an in-flight continuous surge) I was expecting some max exceedance value, after which the engine should be suspected damaged, left at idle and you should land asap. But I take it from your response that this value doesn't exist in any manual and it's simply left to pilot discretion. That surprises me. I wouldn't want to be sitting in 18F, watching a tail of flame for a minute and a half, followed by a resumed climb and a hot section blade to the skull five minutes later. I also wonder if FADEC will limit engine N1 after a serious overtemp event.

There are EGT limits for normal operations, you can find those in the FCOM, but I'm not aware of any set number for an overtemp during or secondary to a surge.

If it's "flaming out the back for a minute and a half", you'll have other abnormal indications besides EGT. Like you said, there are other "vital signs" involved.

[Evan]

The reason you haven't found a definitive answer on the internet is probably because there are too many variables. To wit, for us and our V2500-series engines, the red "tickmark" on the EGT display is OAT-dependent and is not automatically indicative of a hot start. It indicates only that MOC should be contacted. They have a whole set of parameters and limits that they will check against to determine whether a hot start has occurred (or even just an overtemp has occurred).

But you have a digital temp readout as well, so you have an absolute value, right? (BTW, I'm NOT asking about hot start, that was just the precedent I based this on. I'm asking about an in-flight continuous surge) I was expecting some max exceedance value, after which the engine should be suspected damaged, left at idle and you should land asap. But I take it from your response that this value doesn't exist in any manual and it's simply left to pilot discretion. That surprises me. I wouldn't want to be sitting in 18F, watching a tail of flame for a minute and a half, followed by a resumed climb and a hot section blade to the skull five minutes later. I also wonder if FADEC will limit engine N1 after a serious overtemp event.

[ATLcrew]

What is a hot start and have you ever ridden a Jetstream-31?

I parked next to one a couple times.

[ATLcrew]

The internet really has no idea as to where the limit lies with turbofans, which is why I'm asking the question here on the expertnet, but on turboshaft engines like the PT-6, the internet tells me a hot start often results in a costly hot section inspection before the engine is considered safe to return to service. So, I'm extrapolating: if the danger of compressor damage is that significant after a hot start on a turboshaft, isn't it also present on a large turbofan?

The reason you haven't found a definitive answer on the internet is probably because there are too many variables. To wit, for us and our V2500-series engines, the red "tickmark" on the EGT display is OAT-dependent and is not automatically indicative of a hot start. It indicates only that MOC should be contacted. They have a whole set of parameters and limits that they will check against to determine whether a hot start has occurred (or even just an overtemp has occurred).

[Evan]

I'll tell you what's damaged...

This thread. It started as a simple question but I guess nobody has an answer for me.

[3WE]

...PT-6...hot start...

What is a hot start and have you ever ridden a Jetstream-31?

[BoeingBobby]

Sorry, combustor damage, turbine damage, damage.

I'll tell you what's damaged...

[Evan]

Compressor damage? EGT is in the opposite end.

Sorry, combustor damage, turbine damage, damage.

[Gabriel]

... the danger of compressor damage is that significant after a hot start ...

Compressor damage? EGT is in the opposite end.

[Evan]

I really should have known better!

The internet really has no idea as to where the limit lies with turbofans, which is why I'm asking the question here on the expertnet, but on turboshaft engines like the PT-6, the internet tells me a hot start often results in a costly hot section inspection before the engine is considered safe to return to service. So, I'm extrapolating: if the danger of compressor damage is that significant after a hot start on a turboshaft, isn't it also present on a large turbofan?

Now, I realize with pneumatic starters and FADEC and no prop-feather drag, hot starts on turbofans are probably extremely rare, so I'm not surprised if you've never encountered one on a jet aircraft. I also realize that large turbofans are probably designed to be more robust than your typical turboshaft. But there has to be some EGT limit where even a turbofan will require an internal inspection before returning to service. I imagine that limit might also be reached during a full minute or more of recurring engine surge.

[BoeingBobby]

Isn't this the internet?

I really should have known better!

[Evan]

Very interesting, but not correct! This is why you can't always depend on the internet for answers.

Isn't this the internet?

[BoeingBobby]

because a hot start seems to have a shut-down/teardown requirement.

Very interesting, but not correct! This is why you can't always depend on the internet for answers.

[Evan]

No TIT on that family of aircraft either. In fact, I'm not aware of any jets that display TIT.

II suppose it's like medical science, where a handful of vital signs are used to check for more serious conditions throughout the body. If your four primary engine vital signs are good, there's no need for more specific ones like TIT. If there is rise in TIT, that is going to show as a (albeit lower) rise in EGT, Correct me if I'm wrong, but the two cockpit indicators of a continuous engine surge are EPR and EGT. We were taliking about reducing complexity; well that seems like a pretty simple way to recognize the situation (unless, as I believe is the case for the plane you are currently flying, ECAM does that for you).

But again, my question is, if you get a continuous (60-90 sec) surge on climb-out with a corresponding EGT redline, and then the surge self-corrects and the indicators return to normal, do you always return or is there a threshold below which it is considered permissible to continue to your destination? I'm asking because a hot start seems to have a shut-down/teardown requirement.