747-100/200 Brake Overheating
Join Date: May 2000
Location: Seattle
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No.
OPS does not analyze brake heating or heating rate; it only analyzes projected total brake energy absorption for the brake limit part of the equation. If you use up all the projected early by stomping on them at high speed, thereby not allowing air and other drag to do their part, you will use MUCH more brake energy than projected by the analysis. Also, using the energy early means the brakes are absorbing energy at a higher rate, and may not be able to dissipate it quickly enough to the air before the thermal plugs overheat.
OPS does not analyze brake heating or heating rate; it only analyzes projected total brake energy absorption for the brake limit part of the equation. If you use up all the projected early by stomping on them at high speed, thereby not allowing air and other drag to do their part, you will use MUCH more brake energy than projected by the analysis. Also, using the energy early means the brakes are absorbing energy at a higher rate, and may not be able to dissipate it quickly enough to the air before the thermal plugs overheat.
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Join Date: Aug 2010
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Assuming, arguendo, that some classic operators did not use OPS -- they used the old runway analysis charts which, if I'm not mistaken, are predicated on 121.195's stopping within 60% of the runway with maximum braking. That is really all that's required anyway -- the dispatch performance. OPS is nice but really not required by the regulations if you can legally dispatch to the runway under 121.195.
Are you saying that if the pilot actually applies maximum braking when he lands there in order to get the performance guaranteed in the runway analysis, there is no assurance that he will not thermal tires and this is all within the confines of the aircraft certification? Boeing is okay with this?
Are you saying that if the pilot actually applies maximum braking when he lands there in order to get the performance guaranteed in the runway analysis, there is no assurance that he will not thermal tires and this is all within the confines of the aircraft certification? Boeing is okay with this?
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OPS is built around all those charts.
Just because 121.195 sez you have to be able to stop in 60% of the runway, doesn't mean you try to do it on every runway every time. Margins are built in for contingencies and emergencies, NOT for everyday operation. Also, 121.195 does not prohibit Reverse Thrust credit.
Yes, that is effectively what I am saying. Yes, both Boeing and the FAA are "okay with this."
Remember again that the max TOGW rejected takeoff certification is a one-time requirement. The brakes and tires don't have to be usable afterward.
Just because 121.195 sez you have to be able to stop in 60% of the runway, doesn't mean you try to do it on every runway every time. Margins are built in for contingencies and emergencies, NOT for everyday operation. Also, 121.195 does not prohibit Reverse Thrust credit.
Yes, that is effectively what I am saying. Yes, both Boeing and the FAA are "okay with this."
Remember again that the max TOGW rejected takeoff certification is a one-time requirement. The brakes and tires don't have to be usable afterward.
Join Date: Jun 2001
Location: In da north country
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When you apply medium brakes at 163 knots, you are getting the maximum amount of energy into the brakes as soon as possible.
I only have about 5000 hours on the classic, but can assure you, that landing with flaps 30 and no auto brakes and reverse as quickly as you can, you can delay brake application until about 80 knots, and barely have them register in the green.
The problem that I think your "friend" is running into, is the companies SOP of mandating using auto brakes; dumbing down the procedures for the lowest common denominator. I used to regularly NOT use auto brakes, and would often arrive at the chocks with condensation on the brakes.
I only have about 5000 hours on the classic, but can assure you, that landing with flaps 30 and no auto brakes and reverse as quickly as you can, you can delay brake application until about 80 knots, and barely have them register in the green.
The problem that I think your "friend" is running into, is the companies SOP of mandating using auto brakes; dumbing down the procedures for the lowest common denominator. I used to regularly NOT use auto brakes, and would often arrive at the chocks with condensation on the brakes.
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Last I flew the classic 200/300 series 10 years ago. I basically agree with Wiiit Run. I used this exact technique when ever I wanted to exit on closer taxi track without heating breaks. Kabul elevation is 5877 ft. so that will add to the problem.
