smartt1982
Topic Author
Posts: 226
Joined: Sat Nov 24, 2007 11:17 pm

Dispatch Land Reqs 737

Tue Jun 12, 2012 8:31 pm

In regards to dispatch Landing Data (expected Landing weight at your intended destination) prior to take off (For both EU OPS 1 and FAR 121) what is the reason that we include certain things and not others.

For example for all the dispatch landing data, reverser is out right not included in the calculation. I can understand for an expected dry runway we plan during dispatch to land without using credit for reversers. But I cannot understand is, that we do not take the credit for reversers for WET runways or runways that are slippery/contaminated. I know we always look to be conservative but surely we would never go or would be severely comprised if we tried to land on a contaminated runway with no reverse, is there a particular reason we do not take credit for reversers in dispatch. Also on our performance calculations we consider pressure ALT but not temperature or slope of the runway again during dispatch planning.
Just curious about the logic for including some things and not others for dispatch planning.

In relation to calculating Take off Distance. We have the 737NG and on a WET runway with 1x reverser inop we are allowed to take credit for the remaining reverser. But on a take off from a contaminated runway again with 1x reverser inop we are NOT allowed to take credit for the remaining reverser and have to treat it as No reverser available distance calculation.

Any ideas why we would allow it on one type of surface but not the other. Is it something to do with controllability on the ground in the Engine failure case, surely we would still be able to use one?

In regards to Engine Anti Ice on, we calculate a reduction of 300kg in available Take off weight when its on for take off, for anyone familiar with the 737(NG or classic) does this number seem familiar? Is it a generic Boeing number or something our company has come up with. What is the exact reason we need to keep the start switches to CONT when we have Engine Anti Ice on, what is the risk for taking some bleed air for the Anti Ice System?

I know I have thrown in a lot but any info people could chip in would be greatly appreciated.

Cheers
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Dispatch Land Reqs 737

Tue Jun 12, 2012 9:19 pm

Quoting smartt1982 (Thread starter):
I know we always look to be conservative but surely we would never go or would be severely comprised if we tried to land on a contaminated runway with no reverse, is there a particular reason we do not take credit for reversers in dispatch

If a reverser fails in flight, you typically won't know it until you try to use it on landing. By then, it's too late. So you have to assume (most of the time) that the reverser won't work.

Quoting smartt1982 (Thread starter):
Also on our performance calculations we consider pressure ALT but not temperature or slope of the runway again during dispatch planning.
Just curious about the logic for including some things and not others for dispatch planning.

Pressure altitude plays directly into how fast you're actually going. The temperature effect comes in via the pressure altitude (which is really density) so it's covered. Slope will impact how much energy goes into the brakes but now how much distance it takes to stop for a particular autobrake setting. If you're brake-energy limited you should be taking slope into account but that's very rare.

Quoting smartt1982 (Thread starter):
We have the 737NG and on a WET runway with 1x reverser inop we are allowed to take credit for the remaining reverser. But on a take off from a contaminated runway again with 1x reverser inop we are NOT allowed to take credit for the remaining reverser and have to treat it as No reverser available distance calculation.

The 737NG is the oddball in these terms...for some reason it, and it alone as far as I know, allows credit for reversers but only in the case of a wet runway, nowhere else.

Quoting smartt1982 (Thread starter):
In regards to Engine Anti Ice on, we calculate a reduction of 300kg in available Take off weight when its on for take off, for anyone familiar with the 737(NG or classic) does this number seem familiar?

That sounds about right.

Quoting smartt1982 (Thread starter):
Is it a generic Boeing number or something our company has come up with. What is the exact reason we need to keep the start switches to CONT when we have Engine Anti Ice on, what is the risk for taking some bleed air for the Anti Ice System?

Boeing provides the Onboard Performance Tool (and equivalent Boeing Laptop Tool) which takes it into account more accurately but a straight weight increment is a very easy and conservative way to implement the performance penalty. I would guess you go to continuous start with EAI on because you're closer to surging the compressor but that's just a guess.

Tom.

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