Cooling time for PW1100G A320

[pineteam]

Hello guys,

Anyone knows the reason why even during the first flight of the day, there is always engine number 2 who needs cooling time ( Around 45 seconds) while the other engine have no cooling time at all?
Also after a turn around, while starting the engines with dual cooling, engine 2 already started, when setting the engine master 1 to ON, there is always a delay for the engine to actually start and it displays '' cooling'' on the EWD even so the cooling has been completed already and takes a good 15 seconds to actually proceed with the start sequence. It's the same thing while starting the engine during first flight of the day. Even if no cooling required it still do a very short cooling before actually starting. You can see that on this video: https://www.youtube.com/watch?v=4NAs7DJ42eM

Another question: Did you guys notice when you switch off the engines there is a delay about the electrical transient? Is it a sort of protection?

Thank you.

[Nick 1]

Hi ...maybe this , a NEO fadec feature. “ ...the neo FADEC may perform a dry cranking , depending on the thermal state of the engine ,lasting up to 60 second prior to initiating the start sequence ( engine vibration may increase during the dry cranking but should stay below the ‘ amber ‘ display limit in normal operating condition . During dry cranking N2 will be limited to around a maximum of 30 % “

[tdracer]

Maybe related to bowed rotor start mitigation
(see here: https://www.pprune.org/tech-log/635501-a20n-engine-start.html )
Although I can't readily explain why one engine would be meaningful different than the other...

[pineteam]

Although I can't readily explain why one engine would be meaningful different than the other...

Yes that's what is really bugging me. And I know the maintenance was not doing any run up before the first flight of the day so I really don't understand the logic behind.

[Fursty Ferret]

Do you routinely do single-engine taxi on arrival? The bowed rotor motoring is likely dependent on time spent at idle before shutdown, not necessarily temperature at start-up.

[pineteam]

Do you routinely do single-engine taxi on arrival? The bowed rotor motoring is likely dependent on time spent at idle before shutdown, not necessarily temperature at start-up.
Hello Fursty Ferret,
It’s not very common in my company. I personally do it for fuel and brakes saving at some airports but our home base very seldom as the taxi in is generally very short (less than 5 minutes). I did not know that the bowed rotor motoring was linked to how long was the engine on idle on the last flight. Do you suggest that in case of a single engine taxi in after landing, a cooling time of only 3 min and engine 2 shut down might be the reason required for a rotor monitoring only applicable for that engine the next day for the first flight?
Thanks.

[Nick 1]

Some more info ....

“ More publicly highlighted has been the rotor-bowing issue which has meant Lufthansa, IndiGo and GoAir having to endure four-to-five-minute start-up times for each unmodified PW1100G-JM engine which has not had at least two hours’ time to cool down after its previous flight.

In such cases, before starting up, each PW1100G-JM has to undergo a period of low-pressure spool rotation at no more than 10 percent of maximum rotation speed. This is to dispel, by cooling the high-pressure compressor (HPC) module, the thermal gradient which builds up across the HPC. This thermal gradient produced the rotor-bowing issue on the final, eighth HPC stage, which is a one-piece integrally bladed rotor (IBR) produced by P&W. (All eight HPC stages are one-piece IBRs; MTU produces most of them.)

The rotor bowing causes a less-than-optimal clearance between the blade tips of the eighth-stage IBR and the abradable compressor-case lining which surrounds it, reducing the engine’s efficiency.

P&W’s permanent hardware mods for this issue are designed to bring down the maximum cooling time required for the HPC upon engine start-up to 90 seconds per engine, the standard for the V2500-A5 engines powering current-generation A320s.

One P&W fix for the rotor-bowing issue was to add a proprietary, toughened coating of ultra-hardened, ultra-sharp cubic boron nitride (CBN) to the eighth-stage IBR’s blade tips. This CBN coating allows the blades to create a better seal with the casing lining when, intentionally, they cut into the compressor casing’s abradable lining as the high-pressure spool rotates. This reduces HPC efficiency losses.

From engine 770160 onwards, other changes include an improved carbon air-seal assembly around the third-stage HPC bearing. The third-stage and fourth-stage HPC bearings have also been given critical-valve dampers to offset the rotor bow.”

source : https://runwaygirlnetwork.com/2016/06/12/initial-service-problems-of-new-engine-now-over-assures-pratt/

[Fursty Ferret]

Do you suggest that in case of a single engine taxi in after landing, a cooling time of only 3 min and engine 2 shut down might be the reason required for a rotor monitoring only applicable for that engine the next day for the first flight?
Thanks.

To be honest my knowledge is limited to the LEAP. My (limited!) understanding is that the dry motoring allows any warping in the shaft to dissipate at low speed where the vibration won't be excessive.

There may well be an impact on the warping based on three vs five minutes of cooling. But that's only a guess.

[tdracer]

Not familiar with the specifics of what Pratt is doing, but GE/CFM bowed rotor mitigation logic is based on the residual EGT when the next start is initiated.
Subtle things can affect that - the downwind engine will cool slower, as will having one engine closer to the terminal or other building...
Engine guys hate single engine taxi - yes it can save a little fuel burn during taxi (and brake wear in some cases), but I often wonder about it's long term cost benefits. Nice, long cool down times at idle are highly beneficial to engine health.

[pineteam]

Yesterday I flew a Neo and once again same thing: First flight of the day and cooling required only for engine number 2 and nothing for engine 1! No single engine taxi the day before and no engine run up. I asked one maintenance guy he had no clue. Really weird. I guess I will just ask the training department to send an email to Airbus World the reason behind it. :}
https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/378x504/img_8095_15372__6eeaa57e3c7b8c2b38c2da9a12fa62822effea17.jpg

[mantoga_srs]

If I am not wrong, same thing happens on LEAP 1A CFM engine. I will check carefully next time flying a NEO, but I am almost 100% sure. Very interesting.

[AerocatS2A]

This is from my company technical bulletins for the NEO. It seems to answer your question adequately.

3. COOLING Time Displayed on One Engine Only

An erroneous COOLING memo time can display on one engine only, even though both engines were shutdown at same time. This occurs more frequently for the first start of the day, when an engine cooling requirement is not expected.

An errouneous single COOLING memo is caused by the Electronic Engine Controller (EEC) defaulting to a failsafe value for cooling when airplane power was removed overnight.

The erroneous COOLING (motoring) requirement must be met before start. The result is an increased total start time for the affected engine.

New EEC software will correct this issue.

Do you have tech bulletins available?

[pineteam]

AerocatS2A, thank you very much! I was pretty convinced something was not right.
And no I don’t have tech bulletins. One of my instructors friend have access to Airbus World and would help me ask technical questions if required.
If you have any other interesting information about the Neo or A320 family in general to share, please PM me,I would be very interested.
Once again thank you.

[411A NG]

Quite discomforting that something basic like this (power removed from aircraft) is not something that is tested during the development process of a highly safety critical system such as EEC software...

[RogerGliding]

It was probably found during testing, and the management decided it wasn't worth fixing before release.

[TotalBeginner]

Is the dual cooling option available on the LEAP powered NEOs?