Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

landing Perfomance B737NG

Tech Log The very best in practical technical discussion on the web

landing Perfomance B737NG

Old 31st Oct 2008, 17:46
  #1 (permalink)  
Thread Starter
 
Join Date: Oct 2008
Location: bangalore
Age: 55
Posts: 1
Likes: 0
Received 0 Likes on 0 Posts
landing Perfomance B737NG

Recently started flying the jet, the QRH says ldg distances are unfactored what exactly does it signify and factors of 1.67/1.43 have to be done or they have been considered? Perfomance on autobrakes show that the aircraft comes to a halt within the laid down distances.

Also can somebody tell me how to command a constant ROD say 2000fpm descent with VNAV path?
3163micky is offline  
Old 31st Oct 2008, 17:57
  #2 (permalink)  
 
Join Date: Feb 2007
Location: -------
Posts: 478
Likes: 0
Received 0 Likes on 0 Posts
The QRH unfactored distances of the 737 are pure distances from 50 feet above threshold to a complete stop (+/- corrections in case of tail/head wind, reversers inop. etc...). They are in the Performance inflight section and are advisory.The VNAV Path keeps the path between waypoint, rod coming with speeds, if you want a particular rod just use VS, (or Level change with manual throttles;-))FB
Fullblast is offline  
Old 31st Oct 2008, 18:18
  #3 (permalink)  
 
Join Date: Sep 2008
Location: The Middle East
Posts: 118
Likes: 0
Received 0 Likes on 0 Posts
Technically no you don't have to apply the factors to the QRH because the performance is intended to be used in flight, ie after dispatch. The despatch rules do not apply in flight.

The point of VNAV is to give an idle descent from T/D. Not sure why you would want to use VNAV path to descend at a specific ROD, the only way I can think of doing it is to create 2 waypoints with hard altitudes and a set distance apart.

For example, say ground speed of 300kts or 5nm a min, so for 2000fpm RoD, it would take 5 min to loose 10 000ft, in which time you cover 25 nm over the ground. So 2 waypoints seperated vertically by 10 000ft and laterally 25nm would do it. Much easier to use V/S or LVL CHG.
mona lot is offline  
Old 31st Oct 2008, 20:35
  #4 (permalink)  
 
Join Date: Oct 2006
Location: N/a
Posts: 59
Likes: 0
Received 0 Likes on 0 Posts
The disadvantage of V/S and LVL CHG is that any altitude constraints in the route will not be protected. This is particularly important for someone new to type or unfamiliar with company routes etc. An autopilot coupled to VNAV PATH or VNAV SPD will assure compliance. If you are descending in VNAV path and you want to fly a constant ROD for a while, switch to VNAV SPD and over-ride the autothrottles from flight idle into ARM mode. You can then adjust thrust to achieve the required ROD. This is similar to using LVL CHG, except that when a waypoint is sequenced that has an altitude constraint; LVL CHG will bust straight through it. VNAV SPD will revert to VNAV PATH and comply with the restriction.
Artisan is offline  
Old 31st Oct 2008, 22:52
  #5 (permalink)  
 
Join Date: Dec 2002
Location: UK
Posts: 2,463
Likes: 0
Received 9 Likes on 5 Posts
See Takeoff / Landing on Wet, Contaminated and Slippery Runways,
Page 118 onwards, which may help.

Knowing the Distance.
Managing Threats and Errors During Approach and Landing.
AC 91-71 Runway Overrun Prevention.
Landing Performance of Large Transport Aeroplane.
safetypee is online now  
Old 1st Nov 2008, 00:12
  #6 (permalink)  
Moderator
 
Join Date: Apr 2001
Location: various places .....
Posts: 7,195
Received 109 Likes on 70 Posts
Technically no you don't have to apply the factors to the QRH because the performance is intended to be used in flight, ie after dispatch. The despatch rules do not apply in flight.

Perhaps a very simplistically dangerous philosophy ?

In the situation of an abnormal or emergency, the pilot appropriately needs to have a reasonable set of data available for his/her assessment in resolving the recovery. Indeed, it may be necessary (and appropriate, on occasion) for the recovery to involve reduced margins when compared to the normal certification approach.

Keeping in mind that the distance factors are built in to provide a reasonable probability of successfully completing the flight, it is more appropriate for the pilot to

(a) assess all reasonable options

(b) rank the options according to whatever criteria are pertinent to the particular situation

(c) adopt the most appropriate solution for recovery

In respect of landing distance factors, this might come down to comparing multiple available runways .. one should have a good risk-mitigating reason for deciding to use a runway with a significantly lesser factor. If, of course, there is only one runway available then that part of the solution risk assessment can be bypassed ...

The philosophy can be carried across to considerations of any post launch defect situation .. assess and rank the options prior to making the call. One of the resources you have is the MEL .. if you have time to review the MEL, and you choose not to, then I would prefer NOT to be in your shoes at the eventual enquiry if the recovery turns pear-shaped.

The 1.67 factor applies to heavy aircraft scheduled performance while 1.43 normally is for alternate aerodromes if the particular rules permit the distinction.
john_tullamarine is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.