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

Landing Distance Regulation versus RLD?

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

Landing Distance Regulation versus RLD?

Old 23rd Apr 2019, 10:36
  #1 (permalink)  
Thread Starter
 
Join Date: Feb 2015
Location: Middle East
Posts: 103
Landing Distance Regulation versus RLD?

Good Day All,

Regulation states: JET have to stop within 60% of the LDA.

However, when I check the RLD definition from books (Airbus Fcom, Getting to grips with, EFB user guide, company OM)
They used the following calculation:

REQUIRED Ldg distance: DRY
ALD x 1.67 (same as ALD/0,6)

REQUIRED Ldg distance: WET
ALD x 1,92 (same as 1,67 x 1,15)

It seems they multiply the ALD by 60% (which is different)
Any clue??
Feather44 is offline  
Old 23rd Apr 2019, 13:31
  #2 (permalink)  
 
Join Date: Jun 2014
Location: Mordor
Posts: 280
Read again, carefully. The requirement is:

ALD = 0.6*RLD, hence RLD=1.67*ALD.

In other words, you must be able to stop within 60% of available runway, so your minimum runway length is 1.67 times your actual landing distance (derived from performance)
Sidestick_n_Rudder is online now  
Old 23rd Apr 2019, 14:49
  #3 (permalink)  
Thread Starter
 
Join Date: Feb 2015
Location: Middle East
Posts: 103
Hi,
Thanks for help, but still don't get it?

Runway length (LDA): 3000 m
By regulation, I must to come to a complete stop by 1800 m at latest (To stop within 60% of LDA)

Today, rwy is dry and ALD = 1200 m
RLD = 1200 x 1, 67 = 2004 m

I must be wrong somewhere, cause 3000 m is more than correct for a runway and 1200 m ALD is quiet a small value for landing distance.
Feather44 is offline  
Old 23rd Apr 2019, 15:27
  #4 (permalink)  
 
Join Date: Jun 2014
Location: Mordor
Posts: 280
Well, your runway length must be equal or greater than RLD.

E.g.
RLD 2004, RWY length 3000 - O.K
RLD 2004, RWY length 1800 - not o.k.

Look at it this way:
ALD is what your airplane can do under current conditions, assuming short touchdown and maximum braking

RLD is the minimum runway length required for dispatch, with an added margin of 67%

Actual runway length is what your airports has...

ALD values can be surprisingly low, 1200m is not uncommon to see on a dry runway, even on a widebody - but that assumes a perfect landing and maximum braking effort right away - which is not something you normally do in day to day operations. Thatís why you have margins and thatís why for inflight calculations you use OLD (operational landing distance), which has much more conservative values.


Last edited by Sidestick_n_Rudder; 23rd Apr 2019 at 15:44.
Sidestick_n_Rudder is online now  
Old 23rd Apr 2019, 22:44
  #5 (permalink)  
Moderator
 
Join Date: Apr 2001
Location: various places .....
Posts: 6,501
Following on from the previous post,

(a) the actual minimum landing distance is something the test pilots achieved. This was after some dedicated practice work and, even then, the "bad" test runs will be discarded by the OEM TPs and a few more by the backroom aerodynamicists analysing the test results data. The OEM/Regulator TPs will come to agreement on what figures they are going to OK for the aerodynamicists to use in developing the AFM (certification) data.

Having been in aircraft during maximum performance landing tests, might I suggest that you and I, as mere mortal line pilots, are NOT going to achieve what the TPs have put in the AFM as actual figures. That is to say, we will end up in the fudge factor region to a greater or lesser extent, even if we reckon we have done a real beaut job of getting the aircraft on the ground and so forth.

(b) the operationally required landing distance includes fudge factors to provide some fat. Typically, these are 1.67 for dry and 1.67 x 1.15 = 1.92 for wet conditions. Note, if you wish, 1/0.6 = 1.67.

Regulation states: JET have to stop within 60% of the LDA.

Perhaps, providing you read LDR instead of LDA, but let's not read that literally. What it means is that the required AFM landing distance x 0.6 will approximate the flight test actual landing distance. You and I are NOT going to achieve that, as a general rule, regardless of how well we do the task. The statement should be read as "you need to have a 1.67 factor on top of the flight test actual distance achieved for the AFM required landing distance".

Providing the runway LDA is longer than the factored AFM LDR figure then you should be reasonably safe to operate. Do keep in mind, though, runway surface friction characteristics need to be taken into account when considering the landing exercise.

Some jurisdictions permit 1.42 (in lieu of 1.67) for heavy props and alternates but the basic idea remains the same.
john_tullamarine is offline  
Old 23rd Apr 2019, 23:41
  #6 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 64
Posts: 2,343
Originally Posted by john_tullamarine View Post
Having been in aircraft during maximum performance landing tests, might I suggest that you and I, as mere mortal line pilots, are NOT going to achieve what the TPs have put in the AFM as actual figures. That is to say, we will end up in the fudge factor region to a greater or lesser extent, even if we reckon we have done a real beaut job of getting the aircraft on the ground and so forth.
I was on some max performance landing tests many years ago - I don't recall being overly impressed by the pilot skills involved (although the test pilots I flew with were very, very good). What I do recall being impressed by was how fast a big airliner (767) could stop. The deceleration at max braking was amazing - so much so that if there was anything loose around the cabin, it quickly ended up against the forward bulkhead. After coming to a full stop, we'd promptly take off, fly around for 10 or 15 minutes with the gear extended to cool, then we'd do it again.

tdracer is offline  
Old 24th Apr 2019, 00:43
  #7 (permalink)  
Moderator
 
Join Date: Apr 2001
Location: various places .....
Posts: 6,501
That's the size of it. A good TP can make the bird sit up and sing quite nicely. We line folk are a bit more sedate and that routine precludes a reasonable expectation that we can replicate the practised performance of a TP out to get the best data feasible for the OEM.

Sometimes it goes a bit wrong .. eg let a bit too much sinkrate catch you out at minimum speed and it's all over, Red Rover ... (nearly 40 years ago, now).



Did I mention something about line pilot folks not replicating TP performance landing ? Performance takeoff we reasonably can match but not landing ...
john_tullamarine is offline  
Old 24th Apr 2019, 03:24
  #8 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 64
Posts: 2,343
I remember when that MD-80 landing occurred - I worked with a couple people who had previously worked at Douglas/MacDac, and still knew people there. Supposedly, after the tail came off, they rushed the aircraft into to a hanger and closed the door before anyone could get any photos. Didn't work, the next weeks Av Week cover photo was a beautiful shot from about 5 o'clock showing the missing tail and various cables and wiring dangling from the rear bulkhead
If I recall correctly, it was an FAA pilot flying and it was intended to be a 'high sink rate' landing - the target sink rate being something like 6 ft./sec., actual sink rate was about twice that
tdracer is offline  
Old 24th Apr 2019, 03:50
  #9 (permalink)  
Thread Starter
 
Join Date: Feb 2015
Location: Middle East
Posts: 103
Hello,

Yes, I was discusing the "60% LDA" (Literally)
It was my all point.
Why don't they change the wording?

Anyways, thanks for all the interesting info
Feather44 is offline  
Old 24th Apr 2019, 04:16
  #10 (permalink)  
 
Join Date: Jan 2013
Location: Seattle Area
Posts: 65
Originally Posted by tdracer View Post
I remember when that MD-80 landing occurred - I worked with a couple people who had previously worked at Douglas/MacDac, and still knew people there. Supposedly, after the tail came off, they rushed the aircraft into to a hanger and closed the door before anyone could get any photos. Didn't work, the next weeks Av Week cover photo was a beautiful shot from about 5 o'clock showing the missing tail and various cables and wiring dangling from the rear bulkhead
If I recall correctly, it was an FAA pilot flying and it was intended to be a 'high sink rate' landing - the target sink rate being something like 6 ft./sec., actual sink rate was about twice that
That's not how I remembered it, so I looked it up to be sure. The MD pilot was in the left seat and was flying the airplane when this event occurred. Report number NTSB-AAR-82-2, page 2. The 720 fpm sink rate in the final descent was as intended, but he was supposed to flare to an acceptable touchdown sink rate and apparently failed to initiate an aggressive enough pitch up to reduce the descent rate before touchdown.
Dave Therhino is offline  
Old 24th Apr 2019, 04:26
  #11 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 64
Posts: 2,343
Originally Posted by Dave Therhino View Post
That's not how I remembered it, so I looked it up to be sure. The MD pilot was in the left seat and was flying the airplane when this event occurred. Report number NTSB-AAR-82-2, page 2. The 720 fpm sink rate in the final descent was as intended, but he was supposed to flare to an acceptable touchdown sink rate and apparently failed to initiate an aggressive enough pitch up to reduce the descent rate before touchdown.
Am I confusing the pilot part with the incident a couple months later when they spun the MD-80 off the runway (memory says they were doing a landing with some simulated hydraulic failure)? That one wouldn't have been so bad except that they brought in a crane to lift the aircraft back on the runway - but the crane broke and fell on the aircraft essentially cutting it in half

The MD-80 ended up being a good aircraft, but one could have been forgiven for believing the program was cursed during the flight test program
tdracer is offline  
Old 24th Apr 2019, 05:04
  #12 (permalink)  
Moderator
 
Join Date: Apr 2001
Location: various places .....
Posts: 6,501
Yes, I was discusing the 60% LDA

An LDA reference is plain wrong. That's an aerodrome runway number. LDR is the aircraft number.

he was supposed to flare to an acceptable touchdown sink rate

Which is why TPs are far braver than we mere mortals and do heaps of homework to minimise their probability of dying on the job.

Low speed/low energy/high drag state just is one too much of a big, big flare management risk .. which, of course, is why we don't do them on the line.

Am I confusing the pilot part with the incident a couple months later when they spun the MD-80 off the runway

Yep. The sink rate mishap was at Edwards, the hydraulics off mishap at Yuma (and one of the reasons we generally wait until the nosewheel is on the ground before pulling the buckets ..)

Some references

Boy, but does the system sing the TP's praises when he/she gets it right .. but crucifies him/her when he/she screws up. A bit like ordinary line mortal pilot accidents, I guess ...

https://www.ntsb.gov/investigations/...ts/AAR8202.pdf
http://libraryonline.erau.edu/online...s/AAR81-16.pdf
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 © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.