Engine Running
Engine Running.
Grim Reaper Harvesting!
The Invisable Blades Of Death!
Hello my fellow aviators and beloved mechanics. I am doing this article and video on behalf of a request from a flight school. At this flight school a renter stopped the aircraft, and got out to check the wing clearance with a hanger. All the while leaving the engine running! Placing his safety and the security of his aircraft in the hands of the parking brake. These hands of the parking brake may be the very hands of the Grim Reaper!
This is a really bad idea my friends! This is actually ringing the door bell to invite the Grim Reaper to come out to play with you! It is something that you need to train for now. For this will come up in your commercial operations once you get to the flight line. And it does have deadly consequences!
When I was at your stage in my aviation career I was repeatedly told not to leave the parking brakes on. The reason given to me was that the brake lines could rupture due to the temperature changes between night and day. After becoming a aircraft mechanic I routinely maintained the brake lines on many aircraft. These hoses are certified, and are very reliable. I guess one could rupture if left under pressure overnight, but I do not believe this is a valid reason. The valid reason is because the parking brakes on aircraft are just unreliable at best. This is the real reason why we chock the wheels on our aircraft.
What Exactly Are Aircraft Parking Brakes?
The parking brake system on your aircraft is very simple. It consists of just a nydridic reservoir, which feeds the hydridic brake lines, and then a simple check valve to lock in the pressure to hold the brake linings on the rotor.
This is the typical parking brake system on your aircraft. All the components easily fit into the palm of your hand. Notice that it is just inexpensive small rubber "O-rings" holding the pressure on the brakes. These small components are at a disadvantage to hold a aircraft in place. Especially when the aircraft weighs 1,500 pounds or more!
These small components are smaller then your hand, and use tiny rubber ""O-rings" to hold the hydraulic pressure on the brake linings. The parking brake system is subject to many possible failures. Such as low hydraulic levels, or worn out O-rings with cracks or excessive wear.
The hydrulic pressure built up by the master cylinder is then put into the brake caliper. Here the hydrulic pressure pushes against a puck with a O-ring. This puck in turn pushes the brake linings against the rotor attached to the wheel. Once again, these components are small enough to fit into the palm of your hand. This system just is not big enough to hold your 1,500 pound or more aircraft.
The brake caliper on a typical aircraft. You can see how small the caliper is in relation to the aircraft. The photo to the right shows the caliper taken apart. The only thing applying the pressure to the brake linings is the puck in the center. If you look closely you can see the $2.00 black O-ring which is the only real part holding that pressure!
