kaitak
Posts: 9033
Joined: Wed Aug 18, 1999 5:49 am

Descent Rates On Landing: When Could Damage Occur?

Wed Sep 03, 2008 6:23 pm

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"?
 
474218
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RE: Descent Rates On Landing: When Could Damage Occur?

Wed Sep 03, 2008 6:36 pm

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.
 
wilco737
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RE: Descent Rates On Landing: When Could Damage Occur?

Wed Sep 03, 2008 6:40 pm



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)
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2H4
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RE: Descent Rates On Landing: When Could Damage Occur?

Wed Sep 03, 2008 7:06 pm



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
 
wilco737
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RE: Descent Rates On Landing: When Could Damage Occur?

Wed Sep 03, 2008 7:16 pm



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)
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kaitak
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RE: Descent Rates On Landing: When Could Damage Occur?

Thu Sep 04, 2008 4:21 pm

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?
 
wilco737
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RE: Descent Rates On Landing: When Could Damage Occur?

Thu Sep 04, 2008 4:44 pm



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)
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tdscanuck
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RE: Descent Rates On Landing: When Could Damage Occur?

Fri Sep 05, 2008 12:02 am



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.
 
lowrider
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RE: Descent Rates On Landing: When Could Damage Occur?

Fri Sep 05, 2008 1:32 am

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
 
CosmicCruiser
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RE: Descent Rates On Landing: When Could Damage Occur?

Fri Sep 05, 2008 2:51 pm



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.
 
kaitak
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RE: Descent Rates On Landing: When Could Damage Occur?

Sat Sep 06, 2008 2:22 am

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.
 
b767
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RE: Descent Rates On Landing: When Could Damage Occur?

Fri Sep 12, 2008 12:04 am

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.
 
CosmicCruiser
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RE: Descent Rates On Landing: When Could Damage Occur?

Fri Sep 12, 2008 12:13 am



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.
 
lowrider
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RE: Descent Rates On Landing: When Could Damage Occur?

Fri Sep 12, 2008 1:35 pm



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".
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acNDTTech
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RE: Descent Rates On Landing: When Could Damage Occur?

Sat Sep 13, 2008 7:54 am

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.
 
CosmicCruiser
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RE: Descent Rates On Landing: When Could Damage Occur?

Sat Sep 13, 2008 12:40 pm



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.
 
acNDTTech
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RE: Descent Rates On Landing: When Could Damage Occur?

Sat Sep 13, 2008 4:13 pm

Thank you very much for the update.
 
XXXX10
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RE: Descent Rates On Landing: When Could Damage Occur?

Sat Sep 13, 2008 5:29 pm

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.
 
Barnesy2006
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RE: Descent Rates On Landing: When Could Damage Occur?

Tue Sep 16, 2008 3:35 am

I would say about this hard  Wink

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

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