Originally Posted by Terry McCassey
The A345/6 has the parking brakes powered by the blue hydraulic system. The parking brake selector valve, when set, acts as a pressure reducing valve and drops the upstream pressure in the brake lines to 175 bar ( 2535 psi ), this being the pressure that holds the brakes on. The system is designed to hold the aircraft with one engine at full power provided the others are all at idle. All this of course pre-supposes that you have ample blue system pressure to start with !
Originally Posted by F4F
Actually the capacity of the brakes/tires assy being able to hold the aircraft in position at high thrust is proportional to the load of the aircraft, the capacity of the brakes, and the state of the surface (and some other minute parameters)
Originally Posted by Joetom
Normal park brake is only applied to wing gear
Originally Posted by PJ2
The park brake applies pressure only to the main gear and not the center gear ...
The brake pedals apply wheel and center gear brake pressure. The left pedal applies left main brakes plus forward center gear brakes, the right pedal applies right main brakes plus aft center gear brakes.
Given this, the main and center gear wheels would be turning even under maximum pedal deflection, just above the skid point. On-site, there would be signs of heavy braking if indeed it was applied through the pedals, but there would not be skidding.
If the park brake remained set throughout the accident sequence, the wheels would essentially be locked and not turning however.
Originally Posted by Joetom
If park brake was selected on and aircraft moved forward with 4 or more wheels rotating, pressing the toe brakes would have no effect as normal brakes are not avail in said condition.
These are few of the very interesting comments in this thread.
First post on that list mention 2500 PSI regarding the parking brake ... but watching at the BRAKE and ACCU PRESS indicator I cannot see anything much more than 2000 PSI with PARKING BRAKE ON ?
If I well understand, there were only 8 wheels fighting 4 engines set at about 70% N1. How possible would it be for these wheels to be
turning and not skidding under a continuous PARKING BRAKE action ?
Is it possible it would not even leave any braking mark ?
Thanks for your further comments.