Cory6188
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Does A Wet Runway Increase Stopping Distance?

Wed Mar 03, 2004 6:04 am

When I flew from EWR-PBI in November on a 753, we landed in the pouring rain. I could barely see out the windows it was raining so hard. The engines were spewing out water when the thrust reversers were engaged. When we finally turned off the runway, we were at the very end, as there was no more runway left that I could see when we turned to the side.

Does a wet runway greatly increase stopping distance, or was the captain taking it easy with landing? PBI's main runway is 10,000', so it isn't as if we were landing at SNA where you'd need every foot.
 
fspilot747
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RE: Does A Wet Runway Increase Stopping Distance?

Wed Mar 03, 2004 6:05 am

I might be wrong, but I don't believe 753's fly out of SNA. I've only seen 752's.


FSP
 
EMBQA
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RE: Does A Wet Runway Increase Stopping Distance?

Wed Mar 03, 2004 6:14 am

Its a little bit of both..........Wet runways do increase stopping distance, and the flight crew will take it a little more easy on the brakes so as not to hydroplane. Look at it the same way as driving.....when the weather is poor you are taught to increase your braking time when approaching a stop sign. Why, to lesson the chance of hydroplaning and loosing control of the car.
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
QantasA332
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RE: Does A Wet Runway Increase Stopping Distance?

Wed Mar 03, 2004 6:19 am

Does a wet runway greatly increase stopping distance, or was the captain taking it easy with landing?

It certainly does, and can be easily illustrated with the following simple equation:

F= u X n .........where F is the frictional force, "u" is the coefficient of friction, and n is the normal force (sort of the net weight of the aircraft [weight minus lift] for our puposes, if we ignore units). Dry concrete's "u" is 0.7, while concrete under light and heavy rain has a "u" of 0.5 and 0.3, respectively. From this it follows easily that under rain, and the resulting lower values of "u", "F" will also have a lower value and stopping distance would be longer because the landing gear would produce less friction against the runway.

Hope that helps,
QantasA332
 
Cory6188
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RE: Does A Wet Runway Increase Stopping Distance?

Wed Mar 03, 2004 6:25 am

FSPilot747, I didn't mean to imply that 753's land at SNA (they don't). I was just trying to show the fact that PBI is not an airport like SNA where every foot counts, regardless of the aircraft type. 10,000' is a little different than 5400'.
 
Guest

RE: Does A Wet Runway Increase Stopping Distance?

Wed Mar 03, 2004 6:46 am

Yes it does. In the stuff I fly we have to add 15% to the landing distance to account for a wet runway.
 
Cory6188
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RE: Does A Wet Runway Increase Stopping Distance?

Wed Mar 03, 2004 7:09 am

And what, might I ask, be the stuff you fly? There's quite a difference between a Cessna 402 and a 753.  Big grin
 
Guest

RE: Does A Wet Runway Increase Stopping Distance?

Wed Mar 03, 2004 7:26 am

Hi Jetguy, FYI, I believe the gentlemen mentions type ratings,
such as B-737, LR-JET, CE-500, Stuff.
Is Stuff a complex, or complexity...?
xxx
(s) Skipper
 
Guest

RE: Does A Wet Runway Increase Stopping Distance?

Wed Mar 03, 2004 9:50 am

I haven't flown a Cessna 402 in nearly 25 years. (Thank goodness!) I'm typed in 5 different transport category jets and I'm presently current in two bizjets - the Gulfstream G100 and Citation Bravo. It's been 20 years since I last flew a B-727, so that's why I didn't expand my coment to cover it. It's simply been too long since I last flew the '27 and I don't remember it's limitations.

Jetguy

[Edited 2004-03-03 01:54:57]
 
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Starlionblue
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RE: Does A Wet Runway Increase Stopping Distance?

Wed Mar 03, 2004 7:05 pm

SAS is not allowed to land the B738 in Umeå in the rain. The runway is too short. Granted, they try to allocate another AC on those days, but sometimes they have to divert. On dry days it's not a problem.

Taken from an SAS pilot (through my friend the SAS Flight Academy freak).
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
B727-200
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RE: Does A Wet Runway Increase Stopping Distance?

Wed Mar 03, 2004 8:19 pm

Apparently a Cessna Skylane pulls up real quick when there is a couple of inches of water on the runway  Big thumbs up
 
Guest

RE: Does A Wet Runway Increase Stopping Distance?

Wed Mar 03, 2004 9:24 pm

Yes - it increases the distance required.
Read Jetguy's note - 15% is the wet runway factor for landing distances...
xxx
What I am concerned about - for some of you - do you have a driver's license?
Do you know that wet streets or roads increase your stopping distance?
My gosh, if you do not know that... there is a definite problem.
xxx
Many things, that apply to cars, also apply to airplanes... (or v.v.) -
Anti skid system of airplanes = "abs" system of cars...
How about aerodynamics of cars...
xxx
Happy contrails  Smile
(s) Skipper
 
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Starlionblue
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RE: Does A Wet Runway Increase Stopping Distance?

Wed Mar 03, 2004 11:42 pm

Having seen the yearly advent of snow in Sweden, and the smultaneous advent of dozens of cars leaving the road, I am quite convinced that many drivers think that snow or rain is the same as as dry surface.

I can understand the problem if it snow in Sicily, but in Sweden the snow falls every year and slippery surface training with exam is needed to get a driving license.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
osteogenesis
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RE: Does A Wet Runway Increase Stopping Distance?

Thu Mar 04, 2004 12:05 am

Well Skipper,

Of course you are right but the breaking of a car is almost 100% due to the braking of the tires. In an aircraft drag and reverse trust have a much higher contributing factor. And those two are not affected by rain.

Regards,

Osteo
 
Guest

RE: Does A Wet Runway Increase Stopping Distance?

Thu Mar 04, 2004 12:55 am

"...In an aircraft drag and reverse trust have a much higher contributing factor. And those two are not affected by rain."

It never ceases to amaze me when guys whose only "jet" experience is in the left seat of Microsoft's Flight Simulator try and tell guys like Skipper what for.

You add 15% for wet runways. You do not factor in, to the required landing distance, the effect of thrust reversers.

And tell me, just how does the aircraft drag know if the runway is wet or not?

Back to the original post...

The fact that the aircraft turned off the runway near the end means nothing. The pilot could have simply extended his rollout. The 15% that you add for a wet runway is hardly a "show stopper" on most runways that we frequent. For example, if your dry runway requirement is 4000' it increases to 4600' - and that's with maximum effort. In the real world, you don't go around making maximum effort landings. It's not a contest to see who can get the antiskid to kick in the most times. The maintenance guys and the accountants would get on your case before very long. In the real world, you normally moderate your braking effort a bit and you are frequently able to make your "normal" landing distance and runway turnoff just by getting on the brakes a little harder or going into reverse a little deeper.

Jetguy
 
Guest

RE: Does A Wet Runway Increase Stopping Distance?

Thu Mar 04, 2004 1:24 am

Dear Osteo -
xxx
Trouble is, you mention reversers...
They are NOT accounted for in landing and stopping distance computations.
Besides, if you tell me that my landing is based on only 60% of the effective runway length, you are going to tell me that is absolutely enough to stop an airplane... wet or dry runway. And sure, the reversers will always work... or are they...?
xxx
If aviation is a SAFE means of transportation today, it is due to the fact that flight safety is achieved by conservative computations, such as extras for runways required.
xxx
If this discussion was in Civ.Av., I would let it go the way it goes, but here in Tech.Ops., we deal with many friends who are learning to be pilots, and use this source to educate theirselves. I cannot admit wrong statements to be implied as correct facts.
xxx
Happy contrails  Smile
(s) Skipper
 
NWA
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RE: Does A Wet Runway Increase Stopping Distance?

Thu Mar 04, 2004 5:44 am

Right, like jetguy and skipper said, TR are nopt used in the total stopping distance. My question is, for jetguy and skipper, as for required runway distance, how many precent is added on? Like, lets say that the B742 has to have a 10,000 ft runway to take off. It can take off quicker than that, no doubt. I know this all depends on weight and other factors, but how many "saty" precent do they add on? I heard 40%. For instance, if the min rwy length is 10,000, it can get off the ground in 6,000. Is that right? Thanks
23 victor, turn right heading 210, maintain 3000 till established, cleared ILS runwy 24.
 
Guest

RE: Does A Wet Runway Increase Stopping Distance?

Thu Mar 04, 2004 6:10 am

Dear NWA -
xxx
Actually, there has been many discussions about runways for takeoff and landing.
Maybe it is somewhat difficult to research...
xxx
For takeoff, the runway required is the greatest of 3 distances -
(1) Acceleration (all engines), V1 speed, engine fails, airplane stops...
(2) Acceleration (all engines), V1 speed, engine fails, airplane continues and passes 35 ft "obstacle".
(3) Acceleration and takeoff (all engines) passing the 35 ft obstacle + 15%...
xxx
And for landing, we are required to be able to land on 60% of the runway.
But that is coming over an obstacle of 50 ft...
If the runway is wet, we add 15% factor...
xxx
And in "stopping factors"- takeoff abort, or landing, no reversers are used.
Hope this helps you...
xxx
Happy contrails  Smile
(s) Skipper
 
pilotpip
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RE: Does A Wet Runway Increase Stopping Distance?

Thu Mar 04, 2004 7:02 am

Skipper and Jetguy, thanks for sticking up for us low timers in here.

As for stopping distances, they do increase. One of the major problems when landing in a light aircraft on a wet/icy/snowy runway is that we don't have the fancy antiskid systems. In fact, one of the best things to do if you have the runway to permit is not touch the brakes. I like to use as much aerodynamic braking and runway as safely possible to slow down in those circumstances. Each main gear is independently actuated on many aircraft to aid in turning. If you apply pressure at the pedal, and one brake works better, you could be in for a fun ride.
DMI
 
Guest

RE: Does A Wet Runway Increase Stopping Distance?

Thu Mar 04, 2004 7:37 am

Pilotpip - I see your point of view...
xxx
I am a product of the USAF training - Air Force does not believe in thrust reversers.
For a long time, I learned (KC-135) to use aerodynamic braking...
Every landing, was nose high, then hold the controls nose high, very high.
When I did that in the airlines, "they" frowned... - "You gonna hit the tail...!"
I never hit a tail, even in the long body DC8-63/73...
I still do that a lot in the 747...
xxx
In a lightplane, call it C-172, I think it will not hurt much to drag the tail.
But it is not YOUR airplane, so wear the brakes of the guys who rent the plane to you.
One thing in lightplanes, you land on runways probably much longer than required.
You can stop on 1000-2000 ft of concrete, but you got 5000+ ft for you.
With the airliners, you do not have that luxury of much excess runway.
Fly safely, is all I can say to you.
xxx
Happy contrails  Smile
(s) Skipper


 
Guest

RE: Does A Wet Runway Increase Stopping Distance?

Thu Mar 04, 2004 8:12 am

What Skipper said for the 747 applies to the smallest bizjet as well - they're all certified as transport aircraft and the flight crews have to comply with the same regulations when they are operated under Part 121 or Part 135 (commercial operations). Bizjets operated under Part 91 (private) operations have to comply with the basically the same takeoff limitations. (The only difference is a slightly reduced Net Climb Gradient requirement for Part 91 operations.) Part 91 operators don't have the "60% of the landing runway" rule. There are a few other differences, as well, but not many.

I flew off of a joint-use airport for six years. The Air Force operated one of their two F-15 training squadrons there. It was interesting to watch those guys land - as Skipper mentioned, they just held their nose up as long as they could. There were several times, when we were coming back empty, that I would employ aerodynamic braking - much to the delight of the tower guys (they always commented about the "F-15 Rollout") and the chagrin of the copilot (Hey, quit messing around!). It's a good thing that we had a 10,000'+ runway - it's not a very effective way to stop a bizjet. Big grin

Jetguy

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