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Descent Rates On Landing: When Could Damage Occur?  
User currently offlineKaitak From Ireland, joined Aug 1999, 12515 posts, RR: 35
Posted (6 years 1 month 2 weeks 4 days 16 hours ago) and read 12666 times:

Last weekend, I flew FR from DUB to MAN and the landing, oh how shall I put it, was like a brick; it just came down hard ... no bounce, but very firm. It was a perfectly safe landing, probably a good landing technically, but not comfortable.

It got me to thinking, at what point (in terms of feet per second) does a landing start to cause damage. Clearly, a good landing would be 5-10' per second (presumably the oleos would be able to absorb that almost completely), but once you get to around 20-30' per second, you could be looking at fuselage fracturing, possibly the main gear (or nosegear) being pushed up into the landing gear bay?

Also, most airlines (as far as I'm aware) have reports that need to be completed if a hard landing is made. How is this triggered? Is there any report (for example, downloaded from the "Quick Access Recorder" which could tell the crews, "that's above the limit, we need to file a report" - or is it just a question of "that felt bloody rough"?

18 replies: All unread, jump to last
 
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 1, posted (6 years 1 month 2 weeks 4 days 16 hours ago) and read 12671 times:

30 feet per second is 1800 feet per minute, about three times the maximum landing rate.

I have seen major damage done a 18 feet per second or 1080 feet per minute.


User currently offlineWILCO737 From Greenland, joined Jun 2004, 9077 posts, RR: 76
Reply 2, posted (6 years 1 month 2 weeks 4 days 16 hours ago) and read 12667 times:
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Quoting Kaitak (Thread starter):

Airplanes are certified to "survive" hard landings. With max Landing weight (If i remember correctly) it was 600 ft/min and the airplane needs to be fine. With Max take off weight I think it was 360 ft/min upon touchdown. That doesn't soud too much, but 600ft/min is already pretty hard.

For the MD11F we have maximum loads we are allowed to have. 2.25Gs upon touchdown if no sideward movement is there. if there is a sideward movement, then the Gs are lower.

My hardest so far was 1.8 Gs in EMA. Short runway, close to max landing weight and wet runway. So better have a positive touchdown and brake instead of smooth touchdown and overrun the runway  Wink

WILCO737 (MD11F)
 airplane 



It it's not Boeing, I am not going.
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 3, posted (6 years 1 month 2 weeks 4 days 15 hours ago) and read 12651 times:
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Quoting WILCO737 (Reply 2):
My hardest so far was 1.8 Gs in EMA.

So the leaderboard has been installed in the crew room, then?  biggrin 

2H4



Intentionally Left Blank
User currently offlineWILCO737 From Greenland, joined Jun 2004, 9077 posts, RR: 76
Reply 4, posted (6 years 1 month 2 weeks 4 days 15 hours ago) and read 12650 times:
AIRLINERS.NET CREW
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Quoting 2H4 (Reply 3):
So the leaderboard has been installed in the crew room, then? biggrin

 rotfl  Nah, thank god this doesn't exist  Wink But I doubt i would be the leader.

on the 737 my hardest was 1.9 in FAO... Jesus... nobody clapped (at hapag lloyd the passengers usually clapped after landing, but not that day) Big grin
but the aircraft was perfectly fine. no damage, no nothing. we continued to TFS an hour later and then my landing was smoother Big grin

WILCO737 (MD11F)
 airplane 



It it's not Boeing, I am not going.
User currently offlineKaitak From Ireland, joined Aug 1999, 12515 posts, RR: 35
Reply 5, posted (6 years 1 month 2 weeks 3 days 18 hours ago) and read 12484 times:

Thanks folks; much appreciated.

WILCO737, can I just ask about the ref to "G"s; I'm presuming 1G is the landing weight of the aircraft (say 30t, give or take?), so a landing of 1.9G is the equivalent of nearly 60t coming down on the landing gear. At 1G, what kind of descent rate (in feet/sec.) would you have?

Also, where do you get this readout; is it something that can be generated by the FMGS?

Also, given your experience on the MD11 - which as you recall, had a rather unfortunate and annoying habit of flipping over on particularly heavy landings (FedEx at EWR), what kind of Gs or descent rates would result in that?


User currently offlineWILCO737 From Greenland, joined Jun 2004, 9077 posts, RR: 76
Reply 6, posted (6 years 1 month 2 weeks 3 days 17 hours ago) and read 12468 times:
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Quoting Kaitak (Reply 5):
I'm presuming 1G is the landing weight of the aircraft (say 30t, give or take?), so a landing of 1.9G is the equivalent of nearly 60t coming down on the landing gear

Sounds about right. Pretty much double the force on the landing gear.

Quoting Kaitak (Reply 5):
At 1G, what kind of descent rate (in feet/sec.) would you have?

Pretty much zero. Everything above 0 will lead to a G force greater than one. The lowest I had was 1.22 Gs.

Quoting Kaitak (Reply 5):
Also, where do you get this readout; is it something that can be generated by the FMGS?

No, it is not the FMGS. It is the AFDS (but I don't know what it stands for). there you can get hundreds of readouts. And one is VGTD (vertical G at touchdown).

Quoting Kaitak (Reply 5):
Also, given your experience on the MD11 - which as you recall, had a rather unfortunate and annoying habit of flipping over on particularly heavy landings (FedEx at EWR), what kind of Gs or descent rates would result in that?

I don't the facts of this accident - I just know it happened. So I cannot say a lot about it.
sorry

WILCO737 (MD11F)
 airplane 



It it's not Boeing, I am not going.
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 7, posted (6 years 1 month 2 weeks 3 days 10 hours ago) and read 12380 times:



Quoting Kaitak (Reply 5):
(FedEx at EWR), what kind of Gs or descent rates would result in that?

The NTSB report on that accident has all the nauseating details, but most of those MD11 roll-overs were a combination of high descent rates and (relatively) high roll rates at the moment of touchdown. This put a lot of load on the downgoing main gear, causing it to fail. The rest was just dynamics. So it's not just descent rates, it's the vertical speed of the landing gear at touchdown (which is a combination of descent rate and roll rates on all three axes).

Tom.


User currently offlineLowrider From United States of America, joined Jun 2004, 3220 posts, RR: 10
Reply 8, posted (6 years 1 month 2 weeks 3 days 9 hours ago) and read 12366 times:

For the 74 classic, 10 fps (600 fpm) is the max allowable. Anything above that generates the need for a hard landing inspection.


Proud OOTSK member
User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2255 posts, RR: 15
Reply 9, posted (6 years 1 month 2 weeks 2 days 19 hours ago) and read 12287 times:



Quoting Kaitak (Reply 5):
the MD11 - which as you recall, had a rather unfortunate and annoying habit of flipping over on particularly heavy landings (FedEx at EWR), what kind of Gs or descent rates would result in that?

The MD-11 doesn't have an annoying habit of "flipping over". The above mentioned crash as wll as the other MD-10 gear failure had side loads as well. The MD-10 exceeded the design loads of the main gear by abourt 30% when it failed the other gear exceeded the design load by about 10% (I believe) and didn't fail. Both were fiascos in a number of ways none of which was the airplanes fault.


User currently offlineKaitak From Ireland, joined Aug 1999, 12515 posts, RR: 35
Reply 10, posted (6 years 1 month 2 weeks 2 days 8 hours ago) and read 12174 times:

Just noted this in the precis of the crash on the Aviation Safety Network database:

The aircraft touched down 1175 feet down runway 22R at 149 knots with a 500f/min descent rate and 1,67g acceleration. The flight bounced, yawed and rolled right, and touched down again 2275 feet from the threshold, at 1,7g (lateral acceleration 0,4g to the right) and dragging the no. 3 engine 238 feet further on. The right roll, pinning the no. 3 engine to the ground, possibly continued until the right wing's spars broke. The MD-11 skidded off the right side of the runway and ended up on its back 4800 feet from the threshold and just short of Terminal B.


User currently offlineB767 From Norway, joined Feb 2008, 127 posts, RR: 0
Reply 11, posted (6 years 1 month 1 week 3 days 10 hours ago) and read 11939 times:

Just to ask low rider.Isn,t 600ft/min what most airlines have as standard for most of their aircrafts.I have read somewhere that Boeing tested the 747 with sink rates up to 800ft/min during certifications.I remember reading the accident report of a British registrated 747 who hit at nearly 1400 ft/min with only some bent stringers as a resault.

User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2255 posts, RR: 15
Reply 12, posted (6 years 1 month 1 week 3 days 10 hours ago) and read 11935 times:



Quoting Kaitak (Reply 10):
The aircraft touched down 1175 feet down runway 22R at 149 knots with a 500f/min descent rate and 1,67g acceleration. The flight bounced, yawed and rolled right,

As posted before this was not a aircraft problem.


User currently offlineLowrider From United States of America, joined Jun 2004, 3220 posts, RR: 10
Reply 13, posted (6 years 1 month 1 week 2 days 21 hours ago) and read 11849 times:



Quoting B767 (Reply 11):
Just to ask low rider

That is merely the published limitation, with all of the buffers built in. I did not mean to say that the aircraft cannot withstand more, but only what the threshold is for a landing to be considered "hard".



Proud OOTSK member
User currently offlineAcNDTTech From United States of America, joined Jul 2008, 338 posts, RR: 0
Reply 14, posted (6 years 1 month 1 week 2 days 2 hours ago) and read 11782 times:

I was under the impression that the MD-11 was supposed to be flown in the "auto land " mode due to tail strikes when "hand flown." I remember reading that in either Airliners or Airways magazine.

User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2255 posts, RR: 15
Reply 15, posted (6 years 1 month 1 week 1 day 22 hours ago) and read 11759 times:



Quoting AcNDTTech (Reply 14):
I was under the impression that the MD-11 was supposed to be flown in the "auto land " mode due to tail strikes when "hand flown." I remember reading that in either Airliners or Airways magazine.

Not true at all. The airplane lands wonderfully. I rarely make an autoland unless required to. Just think about it...there are certain airports where an autoland is no authorized so what would you do. For example the MD-11 cannot make an autoland at airports above 8000' msl and we fly into TLC (toluca, Mex.) daily where the airport is 8400' msl, no autoland. The DC-10 cannot autoland on 16L/C due to terrain and RA indications.

Many years ago, over 8, the software download did create some "interesting" landings but that is a thing of the past.


User currently offlineAcNDTTech From United States of America, joined Jul 2008, 338 posts, RR: 0
Reply 16, posted (6 years 1 month 1 week 1 day 18 hours ago) and read 11727 times:

Thank you very much for the update.

User currently offlineXXXX10 From United Kingdom, joined Jan 2000, 777 posts, RR: 0
Reply 17, posted (6 years 1 month 1 week 1 day 17 hours ago) and read 11713 times:

I read that AF grounded and later scrapped a Concorde which had previously landed at 14 ft/sec.

The damage was not noticed at the time, but at a subsequent maintenance check.


User currently offlineBarnesy2006 From United Kingdom, joined Feb 2007, 65 posts, RR: 0
Reply 18, posted (6 years 1 month 6 days 7 hours ago) and read 11554 times:

I would say about this hard  Wink

http://www.youtube.com/watch?v=8Pk1N6GzeOo


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