Start Cycle

[trey kule]

I have seen many POHs for turbine powered aircraft that talk of the start cycle time limitations.
But I have never seen anything that defines when the cycle starts or ends.
Simply put, when do you begin and end timing?

I thought I would share this as a training issue.
Our own pilots had a bit of trouble coming to agreement on it, particularily when to end timing.

The best consensus was to start timing when the starter was engaged, and end when the starter reverts to the generator function.
BTW, one has to wonder why no one in the company had an issue with timing before, but was not 100% sure of the start/stop times!
Kudos to the new kid who asked the question...

[Schooner69A]

(Haven't started a turbine engine since '02, so take this with a grain of salt)

Starter timing is only an issue if the engine doesn't start or if you're doing non-ignition ground runs; so, if the engine fires up within the prescribed time limits, then you don't have a problem. i.e. if the engine doesn't fire after three cranking attempts, let the starter cool for five minutes - or something like that. You could run into the starter limitation by trying to flash up a cold-soaked JetRanger where the first attempt didn't bring the engine RPM up to the minimum to introduce fuel. Second attempt better and maybe third attempt successful. (However, the starter limitation may now be secondary to a depleted battery!) (;>0)

In other words, in the case of the helicopter above, it would be something like:

starter limitation: 30 seconds on, 30 seconds off. Repeat twice more, then 30 minute cool. Timing is only critical if the beast doesn't start.

John

[ahramin]

Schooner has nailed it. If you get into a situation where it matters, it will be obvious. It doesn't really matter where the start cycle ends on a normal start, because you aren't going to run the starter again.

[iflyforpie]

I actually have start cycle limitations on my piston starters (Skytech lightweight... not quite as robust as those Prestolite boat anchors). Ten second cranks with a 20 second cool down up to six times.

Timing is with the button/switch depressed or in the start position.... so from 0% until 58% or wherever you disengage the starter. Once you switch to gen, the currents aren't as high because it is shunt wound instead of series wound (which provides maximum starting torque at zero RPM).

Take this with a grain of salt too. I also haven't started a turbine since '02.... and they were massive turbofans with air turbine starter and fully automated APUs.

[Big Pistons Forever]

My last turbine aircraft had Alison 501(D) engines and it only had a "starter" limitation not a "start" limitation. So you timed from starter button in to starter button released.

It would seem to me the issue any turbine engine is ultimately starter motor temperatures. Regardless of whether it is a pure starter or a starer generator the longer the motor is running the hotter it gets. Most engines seem to have 3 tries with 30 seconds between tries and then a long cool down period, restriction.

So I would suggest the start switch on to start switch off is the easiest way to time the start. I would also suggest that the engine should start the first time. If it does not then you need to ask your self "why not" and think about whether a second or third attempt is a good idea, or whether you should consult with maintenance. A lot of turbine engines have been cooked by pilots trying repeated start attempts when they should not have........

Edit: I see IFP beat me to it and he actually knows what he is taking about

[PilotDAR]

I support that this is a "starter energized" limitation - the engine itself does not care. Yes, piston engine starters are getting the limitation specified more, and this is good - you can melt a starter without care. The C310 I used to fly stated the 30s on, 30s off, 30s on, 30s off, 30s on, 30 minutes off.

[trey kule]

I maybe did not pose the question clearly. I will try again.

The starter does have time limitations. They are shown in the AFM.
As a pilot, you can not time it at accurately, unless you know when to begin timing and when to stop or abort.
The engine on most smaller turbines do not automatically abort if the time is exceeded. The engine does not "tell" you that the time has been exceeded.

Which is why the question arose. Exceeding the limits, for example, a bit each time, does not cause immediate catastrophic failure, but could, quite possibly shorten the life of the start/gen.

The result is we have pilots claiming they respect the limitations, but really do not do timings, or actually know the start-stop timing points.

On one machine, the limitation is as short as 20 sec. That is not a lot of time to bring the gas section up to speed, stabilize, introduce fuel, and spool up to stop energizing the starter.

In any event, we thought this was an interesting blind gap in almost all turbine pilots knowledge and practice, though maybe it is only important to our operation.

[Schooner69A]

AFAIK, you start the timing when you hit the "start" button and stop timing when you reach the starter limit; ie around 30 seconds for most as I remember. On a normal start, be it turbine or piston, I've never seen the start cycle exceed its limits.

John

[iflyforpie]

I dunno. I always thought it was SOP, even though I've only run turbines in a maintenance environment. A clock with a sweeping second hand makes it pretty easy, look at it, flick the switch, watch your RPM, add fuel, watch EGT/ITT/TIT, watch RPM, and make sure it makes the point where you cut off the starter in time. If it doesn't, that's a hung start.... no? Turn the fuel off and motor the engine as prescribed and try again or investigate.

As Schooner says, rarely ever comes close. But I was always taught from my first King Air to 727s where starts are measured in minutes to check times..... not just for starting, but acceleration to idle and oil pressure readings too. Maybe the piloting world is different.

[PilotDAR]

The "limitation" for the start cycle may be found one (or both) of two places: Section 2, Limitations, of the flight manual, or in Section 3, Normal Procedures. If you are reading it in Section 2, you are bound by it, and required to assure you comply. If in Section 3, it's a "word to the wise".

For my experience, that "limitation" (however expressed) is there to assure starter motor armature is not damaged by overheating. The most important times are the third 30 second, then the 30 minutes, if it did not start. Exceeding these is where the damage is done.

[pelmet]

As far as I can tell, the question and answers are quite clear.

[DHC-1 Jockey]

On the DH8 it was 1 min on, 2 mins off, 1 min on, 2 mins off, 1 min on, 30 mins off. The time for the 1 minute of starting began once we hit the starter switch, so you had 1 minute from the time you hit the switch until the starter cut out at 63% Nh.

[AOW]

The timing is not so cut and dry in cases where the starter does not automatically disengage. One might argue that if the engine is idling with the starter still engaged, it shouldn't count towards the starter duty limits, since the starter isn't actually doing any work.

[PilotDAR]

Aside from automated turbine engine start systems, with which I have very limited experience, it would be undesirable to have a starter disengage after a period of time. You'd rather over time a starter (and yes, risk shortening it's life) than do an incomplete start, and hang an engine. Unless the auto cutoff for the starter also cut off the fuel, it would invite disaster.

I timed the start of the Allison C-20R today; 37 seconds from switch in to 58%, which is the lower limit. I asked the pilot about the start time, and he told me that starter is 60 seconds, rather than 30.

Like or not, starters are consumable. If you're doing quick start cart starts, it'll save starters. If you're doing long battery starts, you save on the start cart, but pay later for the starter.

[trey kule]

I am glad to see one person is now timing....maybe this training forum has some value.!

You are not in an exclusive crowd. Despite the limitations, most pilots simply do not time starts. Or know when to abort...you have to wonder why the company publishes limitations.

Yes, starters are a consumable. But they should last a reasonable amount of time. If they are treated properly, they will.. But like so many things in the plane, you have to treat them badly for awhile..the abuse does not show up immediately.

Btw.. We actually got a bit of technical expert advice I think....the timing should start when power is applied to the starter, and end when it reverts to gen function...there is a bit of a grey area. You abort if you have not achieved "stable". Ng in the required time...once fuel is introduced, other factors considered if the engine is spooling up you let it exceed the time.
And for those that fly PT6 s.....the 30 sec limitation only applies to battery starts...20 secs with a GPU...and that can be tight if the engine is cold and the starter a bit worn out.
I think there might be a few new turbine pilots reading this that have never actually timed a start.
Might be a good idea...now I will climb down from the apple box, and make my way to the donut box.

[PilotDAR]

the timing should start when power is applied to the starter, and end when it reverts to gen function

If the Flight Manual says so, okay, Otherwise, I don't agree. The timing begins when the starter is energized as a starter, and ends when the start energy is released (you took your finger off the starter button). If the starter is selected to "generator" after that, that is not the end of the start cycle, as the starter may spend time with the engine running, doing neither function (and not heating up).

[trey kule]

Actually, the gen control unit automatically de energizes the starter at a preset Ng., not when you release the starter...the gen trip/reset switch is separate. ..I am sticking to small pratts, so as not to confuse things, and as they are less automated and thus provide a better learning opportunity.

The use of when power is applied to when the starter is energized is a bit of semantics...if you put power to the starter and there is a noticeable lag , that is not a good thing.

[Heliian]

Starter duty cycle starts when the starter is energized and ends when it is de-energized, either by releasing the start button or by an automatic switching feature at a pre-set gas producer speed. It is generally rare with small turbines to exceed the limits during a normal start or even a slow start. Most problems arise during maintenance cranking and repeated failed starts.

Turbine stating tip: DON'T wait for max motor speed or the n1 to level off before introducing fuel. Fuel should be introduced at the a/c's specified speed, as the speed is still increasing. This will give your starter the most battery power to drive the wheels up to speed and produce shorter, cooler starts.

[pelmet]

Some start limits are long enough that they don't need to be timed such as 5 minutes with auto-shutdown that would happen prior to reaching you time limit.

[NotDirty!]

Turbine stating tip: DON'T wait for max motor speed or the n1 to level off before introducing fuel. Fuel should be introduced at the a/c's specified speed, as the speed is still increasing. This will give your starter the most battery power to drive the wheels up to speed and produce shorter, cooler starts.

One-size-fits-all advice is rarely accurate. I would advise to follow established procedures, unless your sample size is large enough to extend this advice to every single PT6, TPE331, Allison whatevertheheck powers B206s, etc.

Actually, the gen control unit automatically de energizes the starter at a preset Ng., not when you release the starter...the gen trip/reset switch is separate. ..I am sticking to small pratts, so as not to confuse things, and as they are less automated and thus provide a better learning opportunity.
...
And for those that fly PT6 s.....the 30 sec limitation only applies to battery starts...20 secs with a GPU...and that can be tight if the engine is cold and the starter a bit worn out.
I think there might be a few new turbine pilots reading this that have never actually timed a start.

Same to you, do you know for a fact that EVERY PT6 gen control unit automatically de-energizes the starter at a preset N1? And start times aren't necessarily those values, and may not change for GPU starts: I fly a PT6 with a 40 second starter duty cycle, and no mention of differences between battery and GPU starts. Even PT6s with the same dash numbers can have different installations in different aircraft that include different accessories that make start procedures different.

[trey kule]

Absolutely correct. I dont know. My original post was in regard to when one knows where the stop limit is reached, but there has been a bit of drift. It is hard to keep things generic, but I tried as much as possible to avoid the....I fly one that.....because it drifts from the original point.

The difficulty is trying to discuss a general issue. For example I had thought I made it fairly clear why I was not referring to Allison or Rolls engines because the start sequence is very different on some..yet a few posts later it pops up...Actually in your post! I also tried to limit it to smaller PT6s.

Such is the internet I guess.

[PHD]

20 seconds is kind of short on a limit isn't it ? which engine is that ?

do you have the option to switch between parrallal to series for acceleration during the sequence to help speed up to the stabalization range.
just thinking shit that's short, 20 seconds fly right by in a flash.

[pelmet]

Starter duty cycle starts when the starter is energized and ends when it is de-energized, either by releasing the start button or by an automatic switching feature at a pre-set gas producer speed.

Exactly.

I would think that because it is so obvious of what the time limit applies to, would be the reason why it is never specifically written down as to what the time limit applies to.

[B208]

Where I'm at the pilot starting calls 'Nh' as soon as the needle moves. The pilot monitoring starts timing off of this mark.

[AOW]

20 seconds is kind of short on a limit isn't it ? which engine is that ?

do you have the option to switch between parrallal to series for acceleration during the sequence to help speed up to the stabalization range.
just thinking shit that's short, 20 seconds fly right by in a flash.

I believe he is referring to the PT6A-114A in the C208. There's only one battery, so no series possibility, but the 20 second limit only applies to GPU starts, so you should have lots of amps and 28 volts to get the job done quickly.