Hydraulics - Gear Flashcards
What is the purpose of having additional wheels/gear?
Better distribution of pavement loading
What is the purpose of the squat switch?
Keeps the gear lever lock ‘locked’, therefore preventing gear retraction on the ground
What happens if the squat switch is faulty?
The pilot can manually override the lever lock and retract the gear.
What is the purpose of an air/ground logic system
Allows the aircraft to understand if it is airborne or on the ground, which will inhibit certain equipment (e.g. gear retraction).
What is the purpose of sequencing valves?
Ensure gear deployment or retraction in the correct order. For example, door opens, gear retracts, then door closes.
After takeoff and having retracted the gear, what position will the gear selector be placed in?
Off (not up). The ‘off’ position prevents excessive buildup of hydraulic pressure and reduces strain on the system.
When the gear selector is placed in the ‘off’ position, what is holding the gear in place since the hydraulic pressure is released?
Mechanical locks.
Explain the process during aircraft pushback
To prevent excessive loads/forces, a locking pin is put in place to prevent crew steering.
What happens if the locking pin is not removed after pushback?
The crew will not have directional control of the nosewheel.
What is an apex pin?
A pin used during towing operations (not pushback). It is stronger than the lockout pin, and is generally used due to the sharp turns required during towing.
In some aircraft, the rudders do not control the nose wheel. Above what speed will rudder inputs be able to control the nosewheel?
Above 80kts (approx). Before this the tiller is required.
What is the purpose of the tiller?
To allow sharp turns during taxi.
When does the steering shutoff valve activate?
After takeoff to stop the wheels being turned after becoming airborne (wheels may not fit in wheel well).
What system ensures that the wheels are straightened after takeoff?
The ‘auto-centre’ system, which uses cams to centre the nose-wheel.
What is the follow-up linkage?
A system which aligns the steering tiller to neutral after takeoff so that the control correctly represents wheel position.
Why does the main gear have steering ability?
To prevent excessive side loads, especially during low speed taxi.
To try and prevent excessive side load stress on the landing gear, what can pilots do?
Avoid sharp turns, especially at low speed.
What direction does the body gear turn?
Opposite to the nose gear
When is body gear steering armed?
During taxi (usually off during takeoff / landing)
What is the purpose of tilting trucks?
Allows wheels to fit into smaller wheel wells
What happens if the tilt actuator is inoperative?
Caution should be used, as damage can occur if the gear does not tilt into the correct position to fit into the wheel well.
A second problem is that some air/ground logic systems rely on the titl system functioning.
What are the two faults which could prevent the landing gear not being retracted properly?
body steering not centred, and tilt actuator not working properly. Note that the pilot can override the system and retract the gear if required.
Are there any alternate means of gear retraction/extension
There is no system for retraction (i.e. if no hydraulics, gear won’t retract).
But for gear extension, an electric system acts as a backup.
For aircraft with 3 sets of landing gear (nose and main gear), there are 3 lights. What about aircraft with 5?
Just 1 light….seriously.
A rear trailing bogie (rear wheels tilted like the A330) is beneficial because it…
Reduces tendency for the nose gear to slam into the ground (i.e. smoother landings)
If a thermal plug melts causing the tyres to deflate, can they just be pumped up again?
No, they should be replaced.
What is the point in having grooves on the tyres?
Deflect water away from the engine intake
Is it normal for the pilot’s brakes to shudder during auto-brake operation?
Yes, this is due to the brakes being ‘modulated’, causing pulses in the hydraulic fluid which is transferred to the pilot pedals
What is the minimum water depth which may lead to hydroplaning?
6mm
What is the main factor affecting hydroplaning?
Tyre pressure. 9 x square root of tyre PSI for rotating wheel, and 7 x square root of tyre PSI for non-rotating. Indicates that non-rotating wheel more likely to hydroplane.
