Engine stabilisation times

[Love_joy]

Folks, currently flying the Dash 8 Q400 which is equipped with the ever faithful Pratt and Whitney PW150's (or at least they have been for me!)

Recently, we introduced single engine taxi both before take off and after landing.

Several colleagues have commented that we don't have a defined stabilisation time for the second engine. If the first officer is particularly keen, we can be setting the power for take-off just about less than 2 mins than post start #1.

Other manufactures publish specific stabilisation times before take-off power should be set, yet for the PW150's I have not found anything.

2 Minutes used to be quoted by some RR old school Trent's.. Any ideas?

[B737900er]

For the Boeing we usually give 3 mins after landing for thermal shock reasons so I would assume it would be similar for engines to.

If your think of it in a practical way would you rev your car engine straight away after turning on for the first time in 12 hours or would you let it run for a bit to get the oil going?

[mcdhu]

Airbus CFM - Company says 2 mins but FCOM is less clear.
mcdhu

[JeroenC]

737NG: 2 minutes before TO.
1 minute minimum before shutdown, 3 minutes recommended.

[Dash8driver1312]

With winter upon us, you want that 55 degrees Celsius anyway if you're taking off into the ice. That does take some time...

On our outfit, we'll taxi out with one feathered but turning, and then unfeather with sufficient time to perform the checklist. That is something like 2 minutes anyway. We're only making single-engine taxiing after landing.

[Tu.114]

The only really limiting figure on the PW150 when it comes to T/O power is engine oil temperature.

In non-icing conditions, takeoff power may be set as soon as oil temperature is above 0°C, which is generally not really a problem to achieve. As my very estimated colleague has written above, the 55°C for departure in or into icing conditions are a different animal and take ages to reach on occasion.

As the oil is mainly heated by the bearings and the RGB, the time it takes to reach that magical number is directly related to engine speed. So in order to speed things up a little bit, taxi with both propellers unfeathered. When standing, placing the power levers ever so slightly behind the DISC gate into the reverse area (minding a possibly slippery ground of course!) will give You a percent or two of compressor speed as well and save some time.

While the time saved by this is certainly noticeable, it still takes ages to get the last few degrees. Do remember this when selecting Your mixture du jour for deicing! Being pennywise and taking only the thinnest possible mixture can come back to bite You in the rear end when You spend all Your hold over time waiting for the oil to heat up and need to come back for a second treatment.

[Nightstop]

Airbus CFM - Company says 2 mins but FCOM is less clear

It's now 3 minutes warm up prior to take off. Something to do with purging of water from the wing section feed gallery on the side of the inoperative engine.

[mcdhu]

Thanks Nightstop.

Do you have the reference for that please?

[Nightstop]

It's in the latest amendment to our OMB (OETD Procedure OMB 2.4.90)

Sorry, can't provide an exact quote due Co. regs.

[tdracer]

At Boeing (where we want to minimize any unnecessary engine wear or deterioration prior to turning the aircraft over to the buyer) we use 5 minutes for both warm-up and cool-down. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/evil.gif
Also remember, for warm-up during winter operating conditions (i.e. really cold) most engines have a minimum oil temp before setting high power.:=

[A Squared]

On our outfit, we'll taxi out with one feathered but turning, and then unfeather with sufficient time to perform the checklist.

What would be the benefit to taxiing around with one running, but feathered?

[No Fly Zone]

While the responses are slightly varied and if there is a common point, I'm reading Engine Oil Temperature as the true measure, not the clock. The Oil Temperature of that second engine, either fully off or a minimum idle, also seems to pass the Common Sense test. While the actual calculation of a time includes multiple other variables that are well above my pay grade, I particularly like @tdracer's note,

"At Boeing (where we want to minimize any unnecessary engine wear or deterioration prior to turning the aircraft over to the buyer) we use 5 minutes for both warm-up and cool-down. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/evil.gif
Also remember, for warm-up during winter operating conditions (i.e. really cold) most engines have a minimum oil temp before setting high power." (Sorry, I could not find the quote button today.) Their use of five minutes seems to meet all of the objectives as well as providing a simple number for line flying. I don't think any operating company will bitch about five minutes when the SOP may say three. And your mileage may vary.

[tdracer]

Oil temp is important, but there are other aspects. Thermal shock of setting high power on a cold engine or shutting down a hot engine can cause compressor or turbine rub and permanent performance loss.


Also, shutting down an engine when it's still really hot can result in fuel or oil coking due to the thermal soak-back - both can have bad long term results.http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/worry.gif I'm referring of course to large turbine engines - no idea how susceptible turboprops might be.

[tmpffisch]

Wouldn't the appropriate source of information be from Pratt or Bombardier?

[Teddy Robinson]

yep it is the engine manufacturer's information that appears in your OMA/B, types differ .. so they have the final call on limitations.

[Going Nowhere]

A Squared,

The fuel flow is about half with the prop feathered.

[A Squared]

Going nowhere, Thanks.

[tdracer]

The fuel flow is about half with the prop feathered.

To bad we can't do that with fan blades :E. Not only potential fuel savings, but we get lots of complaints that the airplane taxis too fast at idle thrust and they need to ride the brakes.

BTW, yes, variable pitch fan blades have been looked at. At least so far, the cost, weight, complexity, and failure modes have made it less than desirable. Plus, to make it really worthwhile would require variable area fan nozzles :uhoh:

[Tu.114]

With regards to stabilisation and warming up of the turbine engine, a difference between a turbojet/fan and a PW150 is the time it takes to get the engine into a condition in which it can deliver takeoff thrust (allow me to use this word for the propeller here as well for operational comparability, although some may certainly cringe at this).

For example, a RR Tay engine takes about 30 seconds from pushing the start select switch until the engine is stabilized and theoretically able to respond to a takeoff power demand. Of course, it is not thoroughly warmed up by then, so a requirement of running it at low power for 2 minutes has been introduced.

A PW150 on the other hand will take the same 30 seconds to get the turbomachinery to run. Then follow about 15 seconds during which the FADEC runs its self test. So after approx. 45 seconds, the engine itself is stabilized. By then, the propeller is of course still feathered and not able to deliver thrust. Unfeathering the propeller will take about another 15 seconds. So it takes a little more than a minute to get a standing engine able to deliver thrust.

Seeing that the Tay is a larger, heavier engine than the PW150, one might get to the conclusion that the longer startup time on the PW will be sufficient to warm the internal parts up, leaving oil temperature as the only real limit that will not be automatically achieved during engine startup.

Just for completeness: before shutting it down, it is required to run the PW150 with the propeller feathered for at least 30 seconds to allow the internal parts to cool a bit and to avoid the things of nastiness tdracer has mentioned. It is a turbine engine after all.

[romero]

the ever faithful Pratt and Whitney PW150's

Not related to your question but some background on the engine which I hope you find interesting.

http://ftp.rta.nato.int/public/PubFullText/RTO/MP/RTO-MP-008/$MP-008-04.pdf
http://www.srs.aero/wordpress/wp-content/uploads/2009/03/srs-tsd-002-rev-1-pw120a-sfc-analysis.pdf

[toumaree]

Cold engine , bold pilot :*

[JammedStab]

The only really limiting figure on the PW150 when it comes to T/O power is engine oil temperature.

In non-icing conditions, takeoff power may be set as soon as oil temperature is above 0°C, which is generally not really a problem to achieve. As my very estimated colleague has written above, the 55°C for departure in or into icing conditions are a different animal and take ages to reach on occasion.



This is what it says for a PW121 engine:

"Oil temperature should be maintained above 71ºC to ensure fuel anti-ice protection. If lower oil temperature are encountered, monitor directly fuel
temperature must be greater than 45ºC to ensure adequate inlet splitter anti-icing."

Errors in sentence structure by ATR.

But, can someone explain the inlet splitter anti-icing for me.

[Tu.114]

Speaking for the PW123 and 150 engines.

See a picture of the PW150 air inlet here: http://www.k-makris.gr/Gallery_2_pics/PW150A_intake.JPG (not embedded due to excessive size). I did not find a similar picture of the 121 or 123 series, but it looks similar enough. There are many vanes, shafts etc. involved that are of course susceptible to icing.

Two methods are used to keep the inlet free of ice: firstly, the intake flange is heated electrically via 115V variable frequency. And secondly, the oil return line from the reduction gear box to the tank is routed through all those vanes to keep them warm. So in order to ensure adequate anti-icing capability, a minimum oil temperature is required.

The requirement of a minimum fuel temperature on the ATR seems a bit odd to me; it must be related to the points of measurement on the engine installation. On the DH8, it is all about the oil temperature.

[tdracer]

Quote:
The requirement of a minimum fuel temperature on the ATR seems a bit odd to me; it must be related to the points of measurement on the engine installation.



I'm not familiar with the specifics of the PW123/150, but a fuel/oil heat exchanger is commonly used to prevent fuel icing - and that takes a minimum oil temp to be effective. So if the oil isn't warm, the fuel can't be cold enough for icing to be a threat.

[Tu.114]

Is the ATR susceptible to fuel icing? The DH8-300 and 400 have a fuel/oil heat exchanger as well, but that subsystem only has limits with regards to fuel or oil temperature associated with it and has no influence on operation in icing condition.

The quote by JammedStab however seems to directly relate fuel temperature to engine intake ice protection.

[Love_joy]

Some great, considered replies. Thanks a mill.

Just another example of how we strike the balance between commercial, safe and efficient operation I guess.

I'm going to take the question direct to P&W, but I predict they come back with the limitations of 0 & 55 degrees.

[No Fly Zone]

When you take this question, I suspect that that will come back with something like this, perhaps in more elegant terms: "Yes, dear pilot, it is mostly about achieving a stable, fully warmed operating temperature, such that all sub-systems are also able to perform their intended functions. When numbers of minutes are specified, this is generally the number of minutes of engine operating time at idle, necessary to make those sub-systems fully functional in most environments." There will likely also be some additional cabbage like, "Those operating in extreme, sub-normal temperatures may wish to extend their engine warming times or even avoid engine shut down all together." and of course, all of that is CYA stuff. In the end, be certain that everything is properly warmed before ordering TO thrust and for our own CYA cabbage, follow the company's SOPs. Company SOP, plus a fudge factor if necessary is really the only way to fully cover your own tender parts. They are not always right, but they are the rules that must be followed, simply because the God of the airways (FAA) has reviewed and approved them. Those rules may suck at times, but they are very real. In this case, you may exceed the SOP by warming a little longer, but there is no defense for undershooting SOP, especially if something goes wrong. 'tis how it is.