A320...Cross-Wind T/O Procedure
 

Hello....

i am wondering why in case of cross wind in excess of 20 kts we have to spool the engine rapidly from 50% N1 to 70% N1 then apply the T/O power.

does it have anything to do with engine stall...or any thing related to the engine...?

thanks

On a normal take off the procedure is to set 50% N1 and when the engines have stabilised set take off thrust. However it is possible that one engine will reach take off thrust before the other creating asymetric thrust. In a crosswind this could lead to possible control problems so by setting 50% and then 70% the chances of temporary differential are reduced.

indeed, Captain Galactic. This is explained in the Normal Procedures - Take Off part of the FCTM (02.050 P10)

Cheers
mcdhu

I believe they got rid of the 70% bit. :cool:

the 70% is still applicable ....

look at FCOM 3.03.12 P1

it' applicable only on CFM engines not on IAE

For IAE V2500 - set 1.05 EPR ( equivalent to about 50% N1), the increase thrust progressively to reach takeoff thrust at 40kts.

Yep, due to harmonic vibration.

IAE engines have a "Keep out Zone" between 50 and 70%. I believe this is due to the possibility of compressor stall in this range with crosswinds. The new procedure is the same as for a normal takeoff.

SIDSTAR Regards the the No-Go zone its actually between 60/61-74 % and its not for compressor stall but for Fan Blade integrity !!

fruitloop & SIDSTAR

Thanks for bringing this (Keep Out Zone) into our attention.

can you guys explain this into further details.

Thanks

Actually no I can't but that won't stop me from trying :}, any spinning mass will have an RPM range that starts vibrating badly and continued operation in this range only makes things worse.

quote....can you guys explain this into further details
Actually i can't either..I believe it has something to do with a transition area where the blades are subjected to more of a Axial load then a Centrifugal..Obviously IAE noticed this harmonics during the testing stage and there-for altered the EEC to stop this range being used.

Airbus recommends rolling takeoffs so If you have a crosswind from the right and you make a right turn onto the runway and apply TOGA power, the fuselage is blocking the airflow to the left engine which could induce a compressor stall at power up so the procedure is calling for the aircraft to be moving forward thus providing a positive flow into the compressor before TOGA power is applied.

This is pretty standard on most planes that I've flown especially the 727 with number 2 engine. You had to get the aircraft rolling with 1 and 3 and then slowly apply number 2 on the roll in a good crosswind scenario ortherwise you could get a compressor stall which always excites the passengers:)

Some background information regarding the keep out zone from the engine manfacturer -
Aircraft: Airbus A320
Engine: V2500-Al Engines through Serial No. V0361
Condition: For stabilized engine ground running within a certain Nl speed range, V2500-Al Engines may have reduced fan flutter margin.
Background: Erosion (blunting) of the blade leading edges reduces the fan flutter margin.
Objective: Restrict steady state engine fan operation in the region (zone) where the flutter can occur. This keep out zone will only be applied to on-ground, static operation (less than 0.07 MN). The keep out zone will not be applied during unrated Nl mode operation, and during thrust reverser operation. The keep out zone is defined as follows:
1.127 to 1.195 EPR MODE
66.1% to 75% N1 RATED MODE
The keep out zone will be implemented as a throttle flat. The following explanation is written in terms of EPR mode operation. The same operational impact applies to the rated Nl mode.
For increasing (acceleration) throttle movement, engine power will be limited to no more than the low end of the keep out zone (1.127 EPR) until EPR command exceeds the high end of the zone (1.195 EPR).
For decreasing (deceleration) throttle movement, engine power will be limited to no less than the high end of the keep out zone (1.195 EPR) until EPR command goes below the low end of the zone (1.127 EPR).

Thanks Ipaq.

You're welcome Dreamland - in fact FCOM 1.70.20 page 4 gives a bit of info about it - see below


Protection against fan flutter
. When on ground at low speed (less than or equal to 0.1 MNI. the Electronic Engine Computer (EECI protects against fan flutter. In so doing. the EEC prevents the engine from being stabilized between an approximate range of 60 % to 74 % Nl (depending on the outside air temperature). Therefore, during engine acceleration on ground, the pilot may notice a non-linear thrust response to thrust lever movement.

Particularly apt as my airline experienced an unnecessary low speed rejected take off when one thrust lever was placed just above the upper limit of the zone and one just below, leading to a relatively large disparity in thrust. Well worth knowing about the IAE no-go zone.

That is suprising. ~10% N1 split on the throttles should have been quite noticable. But these things happen I suppose.

Still one low speed RTO due to the auto keep-out-zone logic is better then over stressing the blades and having to replace engines more frequently...

My company uses CFM engines and we have the same SOP. So I guess this might be a high by-pass ratio jet engine thing rather than just an IAE thing?