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Question About Braking During Landing Roll?  
User currently offlineTu144d From United States of America, joined Apr 2002, 198 posts, RR: 2
Posted (11 years 7 months 2 weeks 5 hours ago) and read 2324 times:

Suppose an aircraft is landing during a rainy period during which the likelihood of skidding is quite high. If the runway is long enough are pilots encouraged to use only thrust reversers and not brakes to avoid skididng even if it means using all runway? Thanks

-Vik-

9 replies: All unread, jump to last
 
User currently offlineN777UA From United States of America, joined Mar 2010, 0 posts, RR: 0
Reply 1, posted (11 years 7 months 2 weeks 4 hours ago) and read 2296 times:

Pilots are entitled to do whatever is necessary to ensure the safe outcome of the flight.

User currently offlineScootertrash From United States of America, joined Aug 2001, 569 posts, RR: 9
Reply 2, posted (11 years 7 months 2 weeks 4 hours ago) and read 2286 times:

I am a runway conservationalist... I don't like to use any more than necessary. That way lots of pavement is available if the sheee-ite hits the fan.

Without the use of brakes (or a minimal amount) the amount of runway you would use would increase fairly dramatically, even with full reverse thrust. My preferred technique is to land to airplane with a minimum amount of float and a little more firmly than usual to ensure all the weight is on the mains. Then I simultaneously apply reverse thrust (well, the props back in beta in my airplane) and evenly apply pressure to the brakes. The anti-skid system should keep the wheels from hydroplaning at that point.


User currently offlineB727-200 From Australia, joined Nov 1999, 1051 posts, RR: 3
Reply 3, posted (11 years 7 months 2 weeks 4 hours ago) and read 2293 times:


Most if not all mainline passenger jets are fitted with ABS, I know all aircraft at Ansett had ABS.

We had one of our BAe146-300's where the ABS was not working. It was a pain in the butt because we had to make sure on the day of operation that it was not going to fly into wet strips. We even had to return the flight a couple of times due to weather upline until the system was fixed.

B727-200.


User currently offlineTop Gun From Canada, joined May 1999, 101 posts, RR: 2
Reply 4, posted (11 years 7 months 1 week 6 days 14 hours ago) and read 2176 times:

I don't like to use brakes when landing. It just wears them down faster. And one must find a way to save money anyway they can. Don't forget kids, TR isn't very useful below 80 Knots (not an exact speed but a good number to use). At that point I use miniamal brakes. I fly into alot of ice/snow covered runways. I like to come in lower on the approach and flair over the button. That way I have maximum runway for landing, because I know braking is going to be bad.

When I go up with my weekend warrior friends, I won't touch the brakes once on landing. (jokes on you, no brakes in a float plane).

Cheers.


User currently offlineJetguy From , joined Dec 1969, posts, RR:
Reply 5, posted (11 years 7 months 1 week 6 days 7 hours ago) and read 2126 times:

Thrust reversers don't stop airplanes, brakes stop airplanes. If I'm flying with a pilot who hasn't learned that basic lesson I won't let him touch the T/Rs at all. I've seen pilots nearly run off the runway while piddling around with the reversers. Many aircraft have minimum speeds at which the reversers can be deployed with anything more than idle reverse power. Get the airplane on the ground, get on the brakes while deploying the T/Rs. Under certain conditions, T/Rs can be very destabilizing and should not be deployed - they will only aggravate weather vaning tendencies. The braking effect of thrust reversers are never included in calculating the runway required for landing. Their effect is only used as a "pad" or "cushion".
Jetguy


User currently offlineAAR90 From United States of America, joined Jan 2000, 3474 posts, RR: 46
Reply 6, posted (11 years 7 months 1 week 6 days 5 hours ago) and read 2105 times:

...are pilots encouraged to use only thrust reversers and not brakes to avoid skididng even if it means using all runway?

Don't know about small planes, but in the airliner world it is the exact opposite. Get the plane firmly on the ground (don't try for a "greaser"), deploy spoilers to put more weight on the wheels (improves brake efficiency) and apply a smooth constant wheel brake pressure (allow Anti-skid to do its job). Reverse thrust as required/recommended. On rear-mounted engine planes (DC9/MD80/F100 especially) judicious [read: cautious] use of reverse thrust is required since the reversed airflow will disturb the airflow to the rudder reducing its effectiveness considerably --MD90 is not so susceptible due to the different reverser design.



*NO CARRIER* -- A Naval Aviator's worst nightmare!
User currently offlineScootertrash From United States of America, joined Aug 2001, 569 posts, RR: 9
Reply 7, posted (11 years 7 months 1 week 6 days 5 hours ago) and read 2103 times:

AAR90:

That is pretty interesting about the rudder instability on the MD90 with reverse thrust... I had no idea that would be true. A cool note to file away just in case I get to fly one.

A side note about reverse in turboprops, especially the Dash 8. Using deep reverse- actually anything below "disc" (the ground idle stop)- is extremely rare. I have never needed it: I only used it in some empty airplane "how short can you land" experements. Lemme tell you... the Dash with near full reverse stops very quickly indeed. The problem is this: You cannot get into full reverse without the elevator bucking so hard that the yoke flies out of your hands. The ATR had the same tendency, but it was possible to get into full reverse because we touched down at a higher airspeed.


User currently offlineAAR90 From United States of America, joined Jan 2000, 3474 posts, RR: 46
Reply 8, posted (11 years 7 months 1 week 5 days 11 hours ago) and read 1999 times:

That is pretty interesting about the rudder instability on the MD90 with reverse thrust...

Aircraft with clamshell reversers redirect the airflow up in front of the rudder area partially blocking the normal airflow to the rudder. For the MD80 & F100 this is a significant concern during landing rollout on wet/slippery surfaces. MD90 has a C-shell reverser (translating sleeve fan reverser) where only fan air is reversed and only a portion of that is directed upward in front of the rudder. Hence it has much better directional control during landing rollouts when compared to the MD80 or F100.

Only times I recall using full reverse thrust on the E-2 Hawkeye was when parking on the Enterprise (CVN65) or during an airshow. Otherwise idle reverse (zero blade angle) was sufficient to stop quickly.



*NO CARRIER* -- A Naval Aviator's worst nightmare!
User currently offlineCx flyboy From Hong Kong, joined Dec 1999, 6604 posts, RR: 55
Reply 9, posted (11 years 7 months 1 week 5 days 10 hours ago) and read 1992 times:

In Cathay we normally allow autobrakes to do the job. Autobrakes are predicated on a deceleration rate only. Autobrake 1 provides the slowest rate and 4 will provide the fastest deceleration rate. MAX will just give you MAX. Because autobrakes 1-4 are giving you a rate, using reversers will not cause you to use less runway. The reverse will help you stop, but the autobrakes will ease off the brakes in order to give you the same rate of deceleration. The same applies if you are landing on an uphill slope. The hill will help you decelerate, so the brakes will ease off to give you the same rate of deceleration as if you were landing on a downhill slope.

Using this logic, you could ague that there is never a need for reverse because it doesn't do anything. Well, on an extremely slippery surface (Where we shouldn't land anyway), reverse will help because the antiskid will release pressure so that the wheels don't skid. It is not impossible that the antiskid system will release so much pressure that you hardly have any braking action. In these conditions you rely on the reverse.

Another case we use reverse is when the runway is wet or very short. In these cases, the autobrakes will mean that we get the same deceleration rate, however having reverse already selected means that we can rely on it if we need it, i.e. if we find that autobrakes are not giving us sufficient braking. The engines on the 777 are very big and take a while to spool up. If you select full reverse when you decide you need it, you won't get it for quite a few seconds.

We always land with idle reverse as a minimum, but normally rely on the autobrakes. It is much cheaper to replace the brakes than it is to replace thrust reverser parts, because we use carbon brakes, and they work better the more you use them.


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