From the question 'Do I Set the Parking Brake On the Ramp?' it is concluded that you do not set the parking brake when parking the aircraft.

The question concerns small aircraft which can be parked for a longer period of time. However, commercial jets (jetliners) are also parked at the gate without the parking brake engaged and rely on blocks/chocks placed around the wheels.

Then why is it called the "parking brake" as it is not used while parking the aircraft? Other wheeled vehicles like cars, trucks and buses are always parked on the parking brake.

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    $\begingroup$ "Other wheeled vehicles like cars, trucks and busses are always parked on the parking brake." Not always. With manual transmissions, some people prefer to leave their car in low gear (first or reverse, depending on whether they're parking uphill or downhill) rather than engaging the parking brake. With automatic transmission, "park" is separate from the parking brake and can be used independently. My understanding is that this is particularly common in cold climates to keep the parking brake from freezing. I'm pretty sure I've seen mention of this on Motor Vehicle Maintenance & Repair, but can't find it now. $\endgroup$ – a CVn Mar 22 '18 at 12:26
  • $\begingroup$ My guess is, you can not really engage the hot bake while standing still for too long. The friction material would bind to the brake surface. I've heard of advice that when a motorcycle comes to a stop light, the rider should use the rear brake while waiting for the light and release the front brake, or the brake pads would bind to the hot disk and leave some residue that can cause the front brake to "pulse". Aircraft brakes may suffer from the same problem, so the parking brake could be only use when the brake is cold. $\endgroup$ – user3528438 Mar 22 '18 at 14:47
  • $\begingroup$ @MichaelKjörling is correct. Automatic transmission vehicles normally do not set the parking brake when parking. Instead, the transmission holds the vehicle in place when 'park' is selected. $\endgroup$ – reirab Jun 27 '18 at 17:00
  • $\begingroup$ @reirab: And then you set the parking brake manually, just to make sure. $\endgroup$ – Sean Jun 6 '19 at 2:51
  • $\begingroup$ @Sean I almost never do that in an automatic unless I'm parked on a steep grade. There's no point. The transmission is plenty to hold the vehicle in place unless the grade is quite steep. Of course, I do set the parking brake when parking a light airplane, as they have no transmission and the wheels will otherwise roll quite freely. $\endgroup$ – reirab Jun 6 '19 at 5:33

Parking brakes are used by commercial aircraft at the gate if the ground crew can not set the chocks. The most common time for this to happen is during a lightning storm when ground crews are not allowed on the ramp. Large airports like DFW have automatic parking lights that will guide the aircraft to the proper alignment and stopping point. The crew will then set the parking brake before deplaning the passengers. Some crews will also use the parking brake for ramp holds, de-icing, etc.

The reason why chocks are preferred over the parking brake, is due to the way parking brakes work on aircraft. On commercial aircraft, the pilots apply the brake manually, then turn on the parking brake, which closes a hydraulic valve trapping the pressurized fluid in the brakes. Due to internal leakage of the valve, the brake pressure will slowly bleed down over a few hours. Therefore, after a few hours the brakes will no longer hold the aircraft. Further, most aircraft ramps are slightly sloped away from the terminal, so the aircraft would end up rolling backwards. Due to the bleed down issues, most airlines require pilots to stay in the cockpit ready to apply brakes until the wheel are chocked.

I have personally seen cases of large aircraft being parked with a parking brake, that rolled after the brake bleed down. In one case, a 777 rolled backwards and the jet-bridge tore off its door. Link to News Article

Car parking brakes work differently. Parking brakes in cars have a direct mechanical linkage (typically a cable) that is held in place. Therefore, they do not have the bleed down issue and will maintain the same amount of braking force at all times.

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    $\begingroup$ Did you mean to write "lightening" (making lighter, reducing weight) and not "lightning" (atmospheric electrical discharges, typically accompanied by thunder)? I strongly suspect that you meant the latter... $\endgroup$ – a CVn Mar 22 '18 at 14:29
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    $\begingroup$ Ditto for "direct mechanical leakage". I think you meant "linkage". $\endgroup$ – Robᵩ Mar 22 '18 at 18:14
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    $\begingroup$ Thanks, I've fixed the typos. Feel free to edit if you see any more. $\endgroup$ – OSUZorba Mar 22 '18 at 19:10
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    $\begingroup$ Does DFW allow the jet bridge operators to work during lightning storms? When we had a lightning storm start at MCO just after we had boarded, but before pushing back, we all just had to sit there for a couple of hours because the ramp closure meant that the tugs couldn't push us back and also that the jet bridge operator couldn't re-attach the bridge until after the lightning stopped. $\endgroup$ – reirab Jun 27 '18 at 18:14

It’s so a linesman can tow your plane around if need be without you being there or needing to get into the plane.

  • $\begingroup$ I understand that this applies to smaller aircraft but the larger commercial aircraft stay at the same gate in general. $\endgroup$ – Brilsmurfffje Mar 22 '18 at 14:28
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    $\begingroup$ @Brilsmurfffje Perhaps that may be true in the majority of cases, but there are significant exceptions. For example, aircraft coming into the terminal for overseas arrivals at JFK are always towed to their respective company terminals after discharging their pax. And the last 747 carrier I flew for had only 3 gates at their headquarters terminal and almost always towed from the gate. Also nose-loading 747 freighters are typically towed away from nose loading ports that lead into a cargo facility. $\endgroup$ – Terry Mar 22 '18 at 17:03
  • $\begingroup$ I would add that chocks are a more reliable - and visible - way to ensure a plane is actually held in place, whether GA or much larger. $\endgroup$ – John Polson Mar 22 '18 at 17:33
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    $\begingroup$ @JohnPolson Be aware that if you have posted a question, it's not at all frowned upon to edit your answer to make it more complete rather than putting it in a comment. $\endgroup$ – Terry Mar 22 '18 at 19:15
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    $\begingroup$ @Brilsmurfffje aircraft are regularly towed from gates to maintenance areas overnight or if their return flight is long enough away that keeping them at the gate would obstruct other flights. $\endgroup$ – jwenting Jun 28 '18 at 10:39

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