PT6A-27 light off sequence

[Hand Commander]

Hey I got a question and I'm curious if anyone else has ever experienced this. The first start of the day, I plug in (we use 24volt battery carts as gpu's which work well) and start the right engine. Everythings normal and stable. Go to start the left engine. Ng stablizes at around 18%, I give it fuel, and it lights off. The T5 temperature increases to around 580 degrees C (well within limits) but then drops about 70 degrees C. Once the secondary nozzles kick in at around 38% NG, the T5 temperature climbs back up to 550 degrees C. Again, the temperature values are well within limits, but it's not normal to see peak T5 temperatures off the primary nozzles and then drop. The right engine peaks after the secondary nozzles kick in as do all the other PT6 powered aircraft I've flown for almost 1000 hours . Engine operation for the rest of the flight is normal and inline with the right engine. This seems to be most pronounced on the first start of the day, but is noticable on subsequent starts to a lesser degree. Both engines are less than 1500 hours since complete overhaul. I'm thinking its some kind of flow divider anamoly (maybe with the 2 pressure cracking valves?) or nozzle issue. I've notified the owner and the mechanic and I'm waiting to hear what they say, but I'm interested to hear from any of you guys. Thanks

 

[erj-145mech]

Whats the electrical load meter doing? I usually wait for it to come down to about .5 before starting the second engine. After the 2nd engine gets around 15-18% turn on the battery as not to blow the current limiters and the operating generator.

Is this on the same engine every morning (first start of the day)?

 

[81Horse]

Have you tried starting the left first? Just for grins ...

 

[Hand Commander]

Whats the electrical load meter doing? I usually wait for it to come down to about .5 before starting the second engine. After the 2nd engine gets around 15-18% turn on the battery as not to blow the current limiters and the operating generator.

Is this on the same engine every morning (first start of the day)?

I use a battery cart for starts which is external power. On the Twotter, there is a battery/external power switch and a DC master switch. A normal start procedure for me is to select external power on the switch which selects the source of power and the DC master switch on which supplies the selected power source to the left bus, then to the right bus via a bus tie switch. The load meter indicates battery/L Gen/R Gen loads so during external starts, the meter indicates 0 since the battery is not being discharged and the generators are not online. The voltmeter will indicate the battery cart voltage and drops initially as the starter switch is activated. Cross generator starts are not allowed on the Otter as per the POH except in an emergency. In order to "turn the battery on" during start, I would have to disconnect the supplied external power in order to engage the battery. Kind of a hazardous move. The battery is normally selected to "on" after the engines have stabilized and the generator lights are on. Once the battery is powering the bus, the generators are brought online.

This is only the left engine on one airplane. I've started a different airplane (a different otter) on the same cart with all normal temperature indications.

 

[Hand Commander]

Have you tried starting the left first? Just for grins ...

Not yet, but I'm kind of thinking it wouldn't really matter. I keep having "hot start" dreams though which are heavily stressing me out while I sleep. But I like the relief of toasting a quarter million dollar engine and waking up to realize it didn't actually happen.

 

[81Horse]

I keep having "hot start" dreams though which are heavily stressing me out while I sleep. But I like the relief of toasting a quarter million dollar engine and waking up to realize it didn't actually happen.

Hah!

This always works for me: write it up, and let a mechanic smoke the engine for you. I never met a mechanic who could resist trying a start himself -- no matter what dire predictions the pilot had to offer.

I have a nice collection of fried blades, etc., and each one tells a little story. The stories all end like this: "I told Maintenance I wasn't going to start that engine again."

 

[Gatorman]

I'm no PT6 guru, but if I were running into problems, I'd have the engine borescopped. It wouldn't cost too much and not too much down time involved. I am sure if you do that, you will find out something wrong. It beats shelling out an engine at altitude.

GATOR