PPRuNe Forums

PPRuNe Forums (https://www.pprune.org/)
-   Tech Log (https://www.pprune.org/tech-log-15/)
-   -   Piper Meridian PT6-42 - Hot start, or not? (https://www.pprune.org/tech-log/592912-piper-meridian-pt6-42-hot-start-not.html)

MeridianPilot 30th Mar 2017 15:15

Piper Meridian PT6-42 - Hot start, or not?
 
Dear all!

A great big hello to everyone! A quick introduction..

I pilot a Avidyne equipped Piper Meridian PA46-500 and I have flown almost 100 hours in my specific aircraft. It is a lovely aircraft and I'm still learning abit more about her every time I fly her. I also hope to share the passion of flying her with you guys here on this forum, which I didn't know existed until I perhaps did something pretty stupid earlier today. I would like to seek some opinions and thoughts as I'm bashing myself up inside.. :ugh:

Earlier today I had a pretty uneventful flight back to my home base and arrived in the evening at around 20:00 LT. Due to needing to drop off a passenger at the terminal, I taxied to the terminal and shut my plane down in a hurry so I could let her off...

I'm quite sure I followed the check list until I used the condition lever to cut fuel and engine shut down. 15% NG and battery off.

Now herein lies the problem.. :ugh:
I assumed the battery was sufficiently charged as I had just landed from a long 3 hour flight..

I assumed ITT has cooled down sufficiently and this is dumb as it was merely 3 minutes.

So I attempted to start the aircraft. I am quite sure I had turned ignition and fuel pumps to manual. I hope I did.

Starter on manual, finger on the starter button.

NG up to 14% and introduce fuel via condition lever.

I notice the ITT skyrocket and saw white smoke come out of the engine! :{

I immediately cut fuel and released the starter. The smoke stopped at this point.

I checked the exceedance page and noticed there was a new exceedance logged being ITT at 1002deg for 00.00.00 seconds. Means fuel was cut pretty quickly I hope.

I realized I must've done something wrong, amongst others.

Noticed the cabin comfort control was still turned on. Turned it off.

Now I went thru the checklist properly to make sure everything is done. Noticed only the cabin comfort was turned on when it should be off.

Saw battery at 23.9v, almost bare minimum.

Attempted to start again. Starter on manual.

Engage starter and smoke starts coming out abit. 14.5% NG introduce fuel and abit more white smoke comes out.

Engine spools up and ITT climbs up to yellow zone BUT within limits this time and stabilizes and comes back down.

60% NG disengage starter and fuel pump and ignition to automatic.

This start was successful.

Only indication anything went wrong was the exceedance logged in the exceedance pages with ITT at 1002deg for 00.00.00.

The white smoke was very very worrying for me though. Wonder if I did something to damage my engine....

I taxied the aircraft for around 2-3 km to the hangar. Around 10 minutes of taxi time. I increased power and decreased a few times, within limits of taxiing just to see if anything gives with the engine and all was good.

I have an engine guy from the service center going to check out the engine tomorrow to be safe. Engine is at 652 hours.

Did I hot start my engine? Did I cause damage to the engine?

What did I do wrong?

Attempting to restart so soon after shutdown when ITT is still hot?

Attempting to start without forgetting to turn off other battery sucking items like cabin comfort control leading to insufficient battery power for start?

Did I forget to engage ignition and fuel pump?

I hope she's okay and I think more than ever now, check list prudence is so so so important no matter how confident I am.

The engine will be checked tomorrow but I read a lot of well thought out opinions from you folks on this forum. Would appreciate your thoughts on what went wrong with the start?

Why was the engine blowing out smoke? Could it be unburnt fuel from the first bad start?

Thanks so much for all the thoughts... much much appreciated.

alphacentauri 31st Mar 2017 03:51

Hi,


I have not flown a Meridian, but I used to fly a PT6 powered PAC750. In my experiences ANY load on the battery will cause the ignition peak temperature to be higher. The more the battery load, the higher the peak ignition ITT. Also the rate of temp increase is higher when there is battery load.


I once tried to restart a PT6 off a battery that was running survey gear and experienced much the same result as yourself. I would suggest that running the cabin comfort system was the cause.


I am not sure what the Meridian checklist says about aborted starts, but with the PAC750 the next start after the aborted start had to be a dry start to remove any unburnt fuel from the system before a live start could be attempted. I would suggest this may be the reason for the high temps on the second start. (Advice: read the manual and checklist on aborted starts)


So far as the white smoke goes......was it actually coming from the exhaust? Or was it coming from outside the engine and filtering past the exhaust stack? Melted nylock nuts make lots of smoke.......


Good that you are getting it inspected, I would suggest sticking a camera in to look at the hot section blades. If they are shiny and clean then you are in the clear. The inspection will reveal whether you have damage or not, and therefore if it was a hot start or not.

TurningFinalRWY36 31st Mar 2017 04:07

any idea how long the starter was running before you introduced fuel?
With many turbines there is a requirement to run the starter for a while to get the ITT and EGT down before fuel is added if the engine was only shutdown recently

chimbu warrior 31st Mar 2017 05:08


Attempting to start without forgetting to turn off other battery sucking items like cabin comfort control leading to insufficient battery power for start?
Not familiar with the Meridian, but have flown other PT-6 powered machines. Is cabin comfort control electrically powered or does it use bleed air? If it uses bleed air, is the valve opened/closed electrically?

I'd be surprised if you have done any lasting damage, but you are wise to have it inspected.

The smoke is mysterious, and the only similar instance I can recall was when having to shut down a PT6 using the fire shutoff (but no extinguisher) due to an issue with the fuel control unit. That created lots of smoke, but no damage.

plhought 31st Mar 2017 05:51

Don't have Engine Manual in front of me, but your exceedance is well within limitations if I recall correctly. It's such a miniscule exceedance it's tough to assess if any damage was done, although I suspect not.

White smoke is not unusual, It's indicative of unburnt fuel. Usually whatever is left in the nozzles that didn't get purged during shut-down.

23.9 Volts is plenty voltage. Many have started a PT-6 with much less, in tougher conditions.

While you should ideally get your quick-turns to 10-15 minutes, I've done plenty a runs where starts and shut-downs were done in very quick succession (rigging/balancing adjustments).

Good PT6 technique with a warm engine is don't look for a specific Ng value to introduce fuel. Keep the thing motoring until you start to see the Ng begin to stabilize. My rule of thumb is once it takes more than a second for Ng to increase 1%, time to introduce fuel. Some will state to wait for fuel introduction until Ng has stabilized.

While what has occurred isn't the best for your engine, with the excellent construction and materials behind the -42s I think you are safe.

stilton 31st Mar 2017 06:27

I would expect there'd be a max ITT for start ?


Haven't operated a PT6 but on the turboprop I flew with the CT7 engine this was a limit,
we would motor the engine to get the temp below this before introducing fuel.

Always good advice to go to max motoring (within starter limits) to get the coole$t possible start as well.

MeridianPilot 31st Mar 2017 09:32

Thank you for all the responses guys, and the reassurance that its highly unlikely something went wrong.

I am getting the engine inspected and cancelling next week's flights whilst that happens. Really prudent to make sure the engine is TIP TOP when you only have 1 to rely on (without going into single vs twin arguments :})


As a rule of thumb, i normally see NG stabilize at 14.6% - 14.9% thereabouts and sort of "slow down" its climb and thats where i introduce fuel.

I know for this start, i would've passed 14% but not sure how far up, obviously not stable yet or the dry cranking would've cooled down the engine sufficiently. Should have cranked abit longer knowing i had a full battery from just arriving back.

stilton : there is, and shame on me, i dont actually know the value off the top of my head. It is in the red zone on the avionics. I often look at the green bar rising into the yellow and i know usually 830 deg - 850 deg is reached before it stabilizes and goes back down and this is in the yellow zone.

The exceedance was 1042 deg, and in the red zone.


plhought : Yes, my problem with this aircraft has always been the battery, or perhaps my battery is not in the best shape.

2 starts back to back without a flight or substantial taxiing is almost impossible without the ITT almost reaching red zone.

I will most definitely take this as a lesson and in future shut down for a minimum of 15 minutes and enjoy the warm musky breeze whilst the turbine cools down. Not worth the sleepless night and pain in my heart. Such is the bond between man and his beloved machine.

I will attempt to do some circuits in the next couple of days once the engine has been looked at before taking long flights just to ensure shes purring like a kitten.


chimbu warrior : The meridian uses bleed air to pressurize the cabin and also mix in some heat, if the cabin comfort control isnt at absolute coldest, at which case is the airconditioning compressor.

I am concerned about the smoke, most of all, as i have had exceedances in the past (2) where ITT rised to 10xx deg too and cut within 1-2 seconds and this was due to attempting to start on a weak battery. Lesson learnt, and never tried again. Both instances though there was no smoke at all so this instance caught me by surprise.

Only difference is this time the engine is mighty hot and past attempts the engine was nice and cool.

TurningFinalRWY36 : I had the starter going for maybe 20-25seconds? Maximum 45 seconds. Just the time taken to get the NG to 14% and fuel went in.

alphacentauri : The white smoke came from the exhaust. Not from the engine itself im quite sure as there is really not much in the way of vents on the PA46 for smoke to escape the engine bay area so you would really see it everywhere but im quite sure i saw it from the exhaust level.

Will have the engine looked at and will plan for 1-2 hours of circuits and landing before taking any serious flights OR passengers in the plane.

I have a nice long 12,000 ft runway so starting at the absolute beginning gives me plenty of time to come back down in the event she quits on the way up.


Thanks alot for the feedback guys, i really appreciate it and the forum/community here is a wealth of information! I look forward to sharing more of my aviation journey here.

If anyone is in my neck of the woods, dont hesitate to hit me up for a flight too. Plenty of beautiful areas here.

I attempted to land the aircraft recently at Tioman Island (ICAO : WMBT) and my oh my, what a challenge that was. Story for another day.... :}

flyhardmo 31st Mar 2017 11:34

As Stilton said let the Ng stabilize for 2-4 seconds before introducing fuel on startup.
The white smoke from the exhaust is most like residule fuel left over from the aborted start. Keep cranking after the aborted start to clear it up to the max starter time limit. You can also have a dry start in before your next proper start attempt to make sure you have cleared all fuel and some of the hot air.
Try parking the aircraft into wind on shutdown and startup. This will help keep the ITT down on startup.
Without knowing the pressurization system on the Meridian I can't comment if that was the cause of the hot start. Chat to your maintenance engineer and get as much info out of them as possible on operation and techniques. Although I don't think the engine is fried I would be interested to know if there is any damage.

RadioSaigon 31st Mar 2017 12:59

God, settle Princesses.... it's a PT-6!!!

It's near bullet-proof, within limits. I don't have personal experience of the -42, but usually have 2-6hrs daily of a -114A or a -140 strapped to my arse. Dare I say it, probably in far more "challenging" situations than implied by the OP. I work in Papua.

There's a thing or 2 strike me straight off the top... 14-ish% Ng is fairly light to be biffing the fuel in. In the -140, I motor to whatever the damn thing will give me, within starter battery/external limits. That's usually in the region of 17+-ish %. I also motor (again within starter limits) to an ITT... on the -140, around 180șC, the -114A, around 150șC before adding fuel. Temps during start Very rarely exceed 780șC.

White smoke during the start speaks to me of excess fuel -as others have said, probably due the lack of a dry motoring run between aborted start and "in anger" start.

ANY compressor bleeds engaged during start -even an open bypass- WILL result in higher-than-normall start ITT's. Not necessarily an issue -and NOT an exceedance until in excess of 1065șC on my engines.

A weak battery most certainly will result in higher than "usual" ITT's... trend-monitoring -and an aware driver- certainly Do have an impact on overall engine health. Batteries generally speaking, do have a very Finite service life, which Will be influenced equally by how often and How the engine is started/run. Your MRO should have a handle on that. Importantly, LISTEN to how your engine starts. Headset off, be aware of how the engine is/is not accelerating, is it reaching a peak then decaying, LOOK at your battery voltage during the start... these are all V important indicators of if/when you should chuck the fuel in. Unfortunately, Voltage is the only battery health indicator we have available... but we rely on AMPS to actually turn the fecking engine. But we don't know that until we ARE turning the engine.

Overall, a PT6 will not shit on you. You really have to work at abusing it before it'll throw its toys out of the cot. Relax. Q's are good -but don't let the OWT's get in your head.

lomapaseo 31st Mar 2017 17:21

damage from ITT exceedance is time and temperature dependent.

I go with what RadioSaigon said.

Piltdown Man 31st Mar 2017 18:27

Just a couple of general things. What does the manufacturer's manual say about quick turnarounds? Do you need to motor the engine before fuel introduction? White smoke is generally unburnt smoke from the previous cycle, whether it be flight or an aborted start cycle. Smelly and on a cold day, very interesting if it lights up! But keep the thing turning. Lastly, do you know the the actions required for a hot start, hung start etc. off the top of your head. Lastly, fuel admission values are generally minimums, not maximums. A lengthy blast with the starter motor will normally bring down temps - but you have to stick to starter cycle limits. I'm sure you'll be OK, PT6s are tough but they do appreciate reasonable batteries.

chimbu warrior 1st Apr 2017 01:32

Might pay to have you battery deep cycled as well.

stilton 1st Apr 2017 06:43

One other thing, it would be much kinder to your battery and you'll get cooler starts
if you use an external electrical power source for the start when available, especially
when your last start cycle was very recent.


Might cost a bit for the use but will pay off over time.

MeridianPilot 1st Apr 2017 08:43

RadioSaigon : Much thanks for the reassurance that the PT6 is indeed built like a tank sir! Helps with sleeping at night although there is that inherent guilt that comes with knowing your irresponsibility with the checklist and hurry to head home may have been catastrophic for my beloved PA46 which whom i cherish very much!

Its been awhile since i cross referenced so for reference sake and knowledge of other Meridian owners, the POH provides :

Introducing fuel after 13% or NG stabilized

The meridian is ok for ITT to rise until 1000 for start, not exceeding 10 seconds, and obviously not very often but isolated incidents is fine, says the POH.

POH says that on aborted starts, dry crank for 15 not exceeding 30 seconds to purge unburnt fuel and also to wait before next start so here is where the mistakes were made.

Although a dry crank then wouldve inadvertently resulted in me not having enough battery for the start thereafter ALTHOUGH it is DEFINITELY better than causing damage to the engine.

I hope shes good, i have the workshop manual on the PT6-42 and guideline for exceedance and at 1,042 deg, less than 5 seconds, it says no action required.

I will upload those pages here so others can refer to them for future reference. Basically it says you have a 5 second window to be a d*ckhead with the engine and thereafter, be prepared to part with your benjamins..

Piltdown Man :

Funny thing is, i have been looking all morning and ive found no guidelines for a quick turnaround on the POH.

You can access a copy of the manual here :-

http://www.pilotinside.com/tools/POH%20PA-46-500TP.pdf

Its not my specific aircraft as its Garmin G1000 equipped but that is just the avionics. All mechanicals remain largely identical with my Avidyne equipped unit.

It does say about dry run for the motor to purge fuel and perhaps cool the ITT down.


I think as a rule of thumb, i will not restart within 20 minutes of powering down and will start only with extreme caution.

I will capture a video of the avionics engine data on my next start and see if i can upload it here to show the vital stats, ITT, NG, Battery etc for a regular Meridian start.. :)

Chimbu Warrior : Yes, i think that may be in order. I want to look at this on my next start and see how weak she gets. Thanks

stilton : External power sources do cost money each and every plug in, but i do see the benefits. Perhaps i can do it when starting from hangar at home base if i buy the ground power unit myself and limit the battery use to all other airports/areas.

As Meridian's dont have much usable load, i cant be carrying a power pack in the aircraft when i fly so mostly this limits me to my homebase hangar.

Will take this suggestion very seriously with much thanks!

stilton 1st Apr 2017 11:10

MPilot,

You're on the right track


However I went back and reread my earlier post, what I said may have implied I was discussing the maximum allowable temp during start and this is critical, but what I wanted to emphasize is the ITT BEFORE introducing fuel is almost as important .I'm sure there's a limit on this and worth memorizing.


The lower temp you have before introducing fuel, max motoring within starter limits plus using external power when available will give you the coolest possible starts, best starter / battery life and most importantly take care of your engine.

MeridianPilot 1st Apr 2017 14:45

Edsbar:

Thankfully exceedances remained well below 5 seconds. Although 3 of them probably isn't very impressive. Will have to make sure we dont add to that list.

The engine blades will be inspected on Monday, i was expecting Friday but the shop didn't get around to doing it. I wont be flying her until she's looked at and will do circuits thereafter first.

As i bought the aircraft used, I'm not too sure about a FSR out here in my neck of the woods. Would i be contacting Piper or Pratt to refer me to a field service representative?

Pardon my inexperience as this is my first "glass cockpit" aircraft.

ADAS would be similar to the CAMP status reports i see on my friends jets right? If this trend monitoring system is available for my Avidyne Meridian, how do i sign up and get it going? So i have in depth knowledge and understanding of what's happening with my plane and the engine.

At this moment, i call the shop over to the hangar every 10-12 hours to do a one over on the aircraft, make sure fluids are okay, brake pads are sufficient, check it through besides the time scheduled maintenance items.

A trend monitoring service would be very helpful and I'd appreciate very much if you could refer me one. Much thanks in advance.


Stilton :

Im going to look at buying that ground power unit sometime next week. Have to arrange someone to be around to disconnect it once start is successful and I'm wondering how hard that might be with the prop blowing away. I cant imagine it's impossible though.

JRBarrett 1st Apr 2017 16:33

As others have mentioned, you should have the battery removed and capacity tested by a qualified shop. I assume the Meridian has a lead-acid battery. These do have a finite service life, and if it fails the cap check, usually the only option is to replace the battery. Your AMM chapter 5, or the battery manufacturer's CMM should give the required cap check/replacement intervals.

That said, 23.9 volts should have been sufficient, but it is the number of amps that the battery can deliver to the starter than really matter.

Using an external GPU (when available) to assist the battery is always a good idea, though I realize that it may involve extra expense, and smaller airports / FBOs may not have one.

plhought 1st Apr 2017 20:46

To the OP - may I suggest swinging by BeechTalk.com. There is an 'other brands' section on those forums and you'll fund great advice and discussion (with real names) over there.

As the -42 is shared between a number of airframes, there's lots of great experience on it.

Personally, I think your battery is a little weak. -42 equipped King Air with a Hawker 40Ah battery I usually see 16-17% NG before it starts to stabilize.

Piltdown Man 2nd Apr 2017 00:18

MP - I gave the manual a quick blast and could find no mention of quick turnarounds or mentions of maximum temps before starting. Therefore it would be reasonable to assume there are none. The relevant limits appear to be a minimum of 13%Ng (stabilised) before fuel introduction and 1,000 deg. As has been written above, the factors affecting a start are battery condition and knobs and buttons, like was the Bleed Lever correctly set? That would certainly boost the ITT.

But slightly digressing, what a lot of aircraft you have got. Most impressive - many toys!

JammedStab 2nd Apr 2017 23:19

All the small PT-6's I flew had a max of 1090 degrees for two seconds as the start limit with much lower for the limit for longer. But I never operated the -42.

In the end, I think that the critical issue is the rpm when the fuel is selected on regardless of battery voltage(although I suppose there has to be enough juice to maintain the rpm once the fuel is introduced).

But, I don't think there is any minimum required temperature or time limit between starts. I am sure that there are plenty of operators that shut down and start up quickly on warm days.

On last thing, if you hear a CB pop during the start, consider an immediate shutdown as a precaution. I know a guy that told me he toasted an engine because the CB for the starter popped at a critical time just at lightoff. If it was something else...no harm done.


All times are GMT. The time now is 16:18.


Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.