Hydraulics - Gear

Question 1

What is the purpose of having additional wheels/gear?

Answer 1

Better distribution of pavement loading

Question 2

What is the purpose of the squat switch?

Answer 2

Keeps the gear lever lock ‘locked’, therefore preventing gear retraction on the ground

Question 3

What happens if the squat switch is faulty?

Answer 3

The pilot can manually override the lever lock and retract the gear.

Question 4

What is the purpose of an air/ground logic system

Answer 4

Allows the aircraft to understand if it is airborne or on the ground, which will inhibit certain equipment (e.g. gear retraction).

Question 5

What is the purpose of sequencing valves?

Answer 5

Ensure gear deployment or retraction in the correct order. For example, door opens, gear retracts, then door closes.

Question 6

After takeoff and having retracted the gear, what position will the gear selector be placed in?

Answer 6

Off (not up). The ‘off’ position prevents excessive buildup of hydraulic pressure and reduces strain on the system.

Question 7

When the gear selector is placed in the ‘off’ position, what is holding the gear in place since the hydraulic pressure is released?

Answer 7

Mechanical locks.

Question 8

Explain the process during aircraft pushback

Answer 8

To prevent excessive loads/forces, a locking pin is put in place to prevent crew steering.

Question 9

What happens if the locking pin is not removed after pushback?

Answer 9

The crew will not have directional control of the nosewheel.

Question 10

What is an apex pin?

Answer 10

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.

Question 11

In some aircraft, the rudders do not control the nose wheel. Above what speed will rudder inputs be able to control the nosewheel?

Answer 11

Above 80kts (approx). Before this the tiller is required.

Question 12

What is the purpose of the tiller?

Answer 12

To allow sharp turns during taxi.

Question 13

When does the steering shutoff valve activate?

Answer 13

After takeoff to stop the wheels being turned after becoming airborne (wheels may not fit in wheel well).

Question 14

What system ensures that the wheels are straightened after takeoff?

Answer 14

The ‘auto-centre’ system, which uses cams to centre the nose-wheel.

Question 15

What is the follow-up linkage?

Answer 15

A system which aligns the steering tiller to neutral after takeoff so that the control correctly represents wheel position.

Question 16

Why does the main gear have steering ability?

Answer 16

To prevent excessive side loads, especially during low speed taxi.

Question 17

To try and prevent excessive side load stress on the landing gear, what can pilots do?

Answer 17

Avoid sharp turns, especially at low speed.

Question 18

What direction does the body gear turn?

Answer 18

Opposite to the nose gear

Question 19

When is body gear steering armed?

Answer 19

During taxi (usually off during takeoff / landing)

Question 20

What is the purpose of tilting trucks?

Answer 20

Allows wheels to fit into smaller wheel wells

Question 21

What happens if the tilt actuator is inoperative?

Answer 21

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.

Question 22

What are the two faults which could prevent the landing gear not being retracted properly?

Answer 22

body steering not centred, and tilt actuator not working properly. Note that the pilot can override the system and retract the gear if required.

Question 23

Are there any alternate means of gear retraction/extension

Answer 23

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.

Question 24

For aircraft with 3 sets of landing gear (nose and main gear), there are 3 lights. What about aircraft with 5?

Answer 24

Just 1 light….seriously.

Question 25

A rear trailing bogie (rear wheels tilted like the A330) is beneficial because it…

Answer 25

Reduces tendency for the nose gear to slam into the ground (i.e. smoother landings)

Question 26

If a thermal plug melts causing the tyres to deflate, can they just be pumped up again?

Answer 26

No, they should be replaced.

Question 27

What is the point in having grooves on the tyres?

Answer 27

Deflect water away from the engine intake

Question 28

Is it normal for the pilot’s brakes to shudder during auto-brake operation?

Answer 28

Yes, this is due to the brakes being ‘modulated’, causing pulses in the hydraulic fluid which is transferred to the pilot pedals

Question 29

What is the minimum water depth which may lead to hydroplaning?

Answer 29

6mm

Question 30

What is the main factor affecting hydroplaning?

Answer 30

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.