737 LGTU & Second Climb Segment

[STBYRUD]

Hello folks,
I had a discussion recently about the function of the landing gear transfer unit on the 737 with my captain - he brought up the point that it assures that the aircraft fulfills the requirements for the second segment climb gradient (2.4%). Of course its supposed to assist in raising the landing gear at a normal speed after failure of the number one engine, but the 737 management reference guide also specifically mentions the second climb segment. Here's what confuses me though - after checking the corresponding JAR literature my memory was serving me right: the second segment begins after the gear has been completely retracted - so how does the retraction speed of the gear influence the second segment gradient at all? Am I missing something vital here?

Thanks in advance, hope that I don't completely embarass myself with this question

[Sciolistes]

I would have thought it is the 3rd segment which would be compromised as JAR expects that to be "measurably positive" with the landing gear retracted. Also, net performance requirements expect the 3rd segment to be completed within 5 mins.

[rudderrudderrat]

Hi STBYRUD,

The second segment begins from 35 ft above the clearway at a speed of V2, and ends not below 400 feet. You are allowed to have the gear raised during the second segment.

Whether your gear is up or down, changes the gradient you will achieve.

[dpk737]

The second segment begins with Gears retracted. Thus, LGTU helps to retract gears, in case #1 engines fails, so that 2nd segment can start on time. In case if this feature was not there, then in case of #1 engine failure ( that is EDP system A ) the gears would take much longer time to retract. This would extend First segment and delay second segment, which would have an adverse effect on Take off thrust time limit.

I hope this makes sense!
Safe landings.

[Old Smokey]

Prooners, skip straight from the first post to the last by dpk737, therein lies the truth Nice work dpk737, and welcome to PPRuNe.

If I might expand slightly on one of your comments -"This would extend First segment and delay second segment". Yes, absolutely true. The delay in commencing the 2nd segment is not so much the issue, it's the fact that extending 1st Segment distance would place the aircraft beneath the "normal" 2nd segment profile with attendant obstacle clearance ramifications. Hence the importance of "normalising" 1st Segment, in the interests of retaining the integrity of the 2nd Segment.

Nice work for your first post, may you make many more!!!

Regards,

Old Smokey

[rudderrudderrat]

gear down ferry flight

Hi,

Good answer from dpk737.

My performance section of FCOM refers to the second segment climb during a gear down ferry flight - is this an oxymoron?

[411A]

My performance section of FCOM refers to the second segment climb during a gear down ferry flight - is this an oxymoron?

Negative.
These ops are allowed, weight permitting...however, can be quite restrictive.

[dpk737]

Thanks Old Smokey