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PorcoRosso
14th Feb 2003, 09:14
My company is in the process to buy a twin turboprop, equipped with PT6
I was warned that some PT6 are better than the others, and therefore to be cautious with PT6-A28, and choos preferably an A/C equipped with PT6-A34
As I am new in the turboprop business, I am seeking for specialists advices.
What is the maximum TBO on those types ? when should you have an HSI ? under which condition could you extend their TBO's ....etc..etc ...

Many thanks

PorcoRosso
14th Feb 2003, 11:49
Thanks for the link, Lear 23 .
Any comments from engineers ?

411A
14th Feb 2003, 17:25
Operated PT6 powered aircraft when they first became available in the USA (1966...DHC6 and BE99) and found the engines to be very rugged and reliable.
The commuter airline that I flew for at the time had 32 twin otters and 15 BE99's, with a large variation of pilots, older military guys and younger civvy guys.
The FAA allowed on-condition maintenance after about three years of operation, with hot section inspections at each 1800 hours, as I recall. Overhaul was at 4400 hours.
Some of the older military guys paid no attention to the torque meter, preferring to set power by ITT and RPM (it worked on the B47, so should also work on the PT6). This practice is most definately frowned upon by Pratt&Whitney, and leads eventually to power turbine/gearbox failures.
The only engine failure that I recall was just after takeoff at 200agl, the prop governor pilot shaft sheared, and the prop feathered automatically (no oil pressure to prop, feather results).
Hope this has been of assistance.

PorcoRosso
14th Feb 2003, 20:56
It is 411A !
Your advices are appreciated.
Do you know anything about the PT6 fitted on Piper Cheyenne, as it would probably be the twin my company gonna buy ?

Best regards

411A
15th Feb 2003, 00:50
Believe the Cheyenne I & II are fitted with the PT6A-27, same as the DHC6 and BE99, altho possibly the PT6A-20. However, uprated engines may have also been fitted by STC.
Either engine is more or less bullet-proof.
FCU and propeller governor rigging is very important, and is best left to those that know how.

Make sure the ships battery is well charged for starting, and follow the AFM with regard to charging between engine starts.

These engines, altho of an old design work good, and last a long time.

Squawk7777
15th Feb 2003, 02:20
I cannot really comment on the engines, but the Cheyenne (1) I flew a little while back seemed a bit unstable compared to the King Air. The reason I remember is that the CAA did not like the Cheyenne I when Piper wanted to certify it in the UK.

The only other thing regarding PT-6 operation is that you have to watch out for visible moisture and a temperature range around freezing. That's one of the differences between piston and turboprop/jet flying. We actually had a power turbine blade damage (just one blade) whether it resulted from flying in cold and moist weather (=ice) I don't know.

Sheep Guts
15th Feb 2003, 21:14
Porco Rosso,
Just to add to 411as good post. The PT6A-20s and the PT6A- 27 s and 28s ,are somewhat different engines, but only slightly.
The -20 the first one fitted to DHC-6-100/200 and B90 s have a tendancey to be temp limited especially in Tropical climates. They also start hotter due to of a single stage fuel nozzles. And because of this their life is shorter, especially without Trend monitoring carried out. Be sure you boss gets Trend Monitoring, put in place, as it will save him litterally tens of thousands of US dollars. An extension from 3500hrs to 5000hrs is alot of money and time saved. Something they dont even do where I am, but thats another story....

The -27S AND -28S on the other hand arent as limited. That means you should still use a Torque meter and computer to work out T/O settings especially in hot regions. The -27S have dual stage fuel nozzeles 7 primary amd 7 secondary ( out of the DHC-6-300 Manual). So in effect there is a staggered light off you get 2 peaks one at around 20-26% ng or n1 and the second light off at around 35% to 40%ng or n1.( this reduces the start temp compared to the older -20, hence I think the reason for the mod) On on a -27 or 28 , you dont release the starter until the 52% and the Ng is self sustaining.

Turbine life is inversally proportional to the number of warm starts or temp limit breaches.

Just for handling the engine. The main care I like to see, is advance the powerlevers gently until around 60%ng or n1 or greater after which there shouldnt be a problem moving them faster from there on. Otherwise youll dump in too much fuel too early and breach a limit. Also reduces engine life. Where I am at the moment alot of F/Os are handling them like a recip, you cant really.

Now in saying that ,allways ensure you have the correct Voltage available and a good GPU. Otherwise you could breach a limit.

The Pratt site mentioned above is good reading also.


Regards
Sheep

I think though from the -27 onwards I think they are a very robust engine. Treat it like you would your mother, and it will give you back the same.:)

Your question as to what are -34S LIKE , not sure myself. But I know they are fitted to EMB-110 Banderante. So any Bandit Pilots out there can add info on the -34?

To add to what another person has, said ensure that its on your UK CAA Approval list of Types, as they have banned some Turbo Props, not sure why.

Captain Stable
16th Feb 2003, 08:52
The PT6A is one of the most reliable, rugged turboprop engines you can get. Loved it.

I heard of one case a few years ago in which a Kingair of some variety landed somewhere in S Africa in the bush with some sort of problem - can't remember what. The pilot (somewhat hurriedly) shut the engines down and leapt out (he was on his own in the aircraft and as he vacated the area upwind, realised he had not completely shut down one engine, since it was still running. Rather than climb through the aircraft to the cockpit, he reached inside the door and pulled out his hunting rifle, and fired it into the engine until it stopped.

Whatever the problem had been, it was spurious. The pilot was rescued shortly thereafter, as was the aircraft, which had no damage whatsoever except that one of its engines had been shot to death! :eek:

PorcoRosso
16th Feb 2003, 13:47
Sheep Guts
That's an explanation ! Exactly what I was looking for !
Many thanks for this long winded but fascinating post. As I am not used to turboprop yet, this kind of infos is very useful.
I'll let you know what type of Cheyenne and engines we'll finally get.
About the CAA approved A/C list, we won't have any problem since the Cheyenne will be on the "N" register.
As far as I know the Cheyenne 2 was not certified in UK, due to instability problems related to the ...Stability Augmentation System ;)
Anybody on this one ?

Airking
16th Feb 2003, 20:43
Hi Porco,
the stability augmentation system stability through tension changes in the elevator downspring (you have to pull harder near to stall)
A sensing vane (r/h nose) provides AOA info to the computer, that applies steering signals to the Downspring servo actuator and to the stall margin indicator and stall warning horn.
Then youŽll find a SAS overide in case of malfunction...
BTW, altitude loss for stall is 750 feet...(about 4 times of what you need in a KingAir 200!!!)
A/C may sit on its tail, if no counterweight is placed in Nose !
(Powerback is another nono if 8th seat is occupied)
Generally W&B is not so easy in a cheyenne II, watch it carefully.


Engines on the -II are -28, 620 SHP.

Starter off at 52%(-I,-II,/56%-IIXL), anything below is dangerous ! (watch for ITT to stabilize or better drop before turning off the starter
As pointed out before, ALWAYS have a good battery or GPU. Better have it deepcycled more often than in the manual to ensure good condition.(applies to all turbine ops)
DonŽt drain your batt by using lights and other gizmos too long while waiting for eng start, most Engines that suffer damage get it during starting with low volts...
YouŽll find out, that moving powerlevers gently is always good on PT6ses, there is no need to rush anyway since the -II is definetely NOT underpowered.
Yours
Airking

:ok:

PorcoRosso
17th Feb 2003, 09:16
AirKing
thank you for the tips on the Cheyenne, I remember you gave me a lot of useful info last year concerning the Cheyenne.
For some reasons, it took my boss more time to set up the leasing agreements and so on ... We were in the process to buy a TBM700 instead of a Cheyenne, but due to various problems, we are moving back toward this machine.
I will contact you shortly since I will need other tips concerning this machine. I am not hearing the same song from the potential seller, so I'd like to have an operator appreciation as well ;)

Best regards

Sheep Guts
18th Feb 2003, 23:39
Porco ROsso,
I must amend, my previouys post. Air King is definitely right. You allways hold the started until 52% Idle is achieved and self sustaining.

Ofcourse I was refering to the TwinOtter and for which I beleive Ive made an error. oops


Regards
Sheep:p

I allways stand corrected.

:)