Jacking Procedure-Lowering

The general procedure for lowering the complete aircraft on jacks is as follows:

1        Ensure that the landing gear control lever in the cockpit is selected to the ‘Down’ position.

2        Ensure that Ground Safety Locks are fitted on all Landing Gears.

3        Ensure that the Brakes are released.

4        Ensure that all the passenger/crew doors, the emergency exits and the cargo doors are closed and locked or fully open and locked.

5        Clear the area around the aircraft of all ground support and maintenance equipment and ensure that no other work is being carried out.

6        Loosen the jack Safety Locking Collars.

7        Slowly operate the jacks to lower the aircraft at the same time to keeping the aircraft level until all the landing gear wheels support the full weight of the aircraft.

8        Ensure that throughout the jacking operations the jack Safety Locking Collars are kept approximately 2.5 cms clear of the jack body.

9        When the jack rams have ‘fully’ withdrawn into their jack bodies the jacks may then be removed from under the aircraft.  The removal of jacks prior to this point can be dangerous if the aircraft suddenly settles owing to any ‘stiction’ in the landing gears.

10      Apply the Brakes.

11      Fit Wheel Chocks.

12      Reinstate the relevant circuit breakers deactivated prior to raising the aircraft.  Restoring the aircraft to the ‘Ground Configuration’.

13      Remove warning notices from the aircraft cockpit.

14      Remove Safety Barriers from around the aircraft.

Jacking Procedure-Raising

The general procedure for raising the complete aircraft on jacks is as follows:

1        Place Safety Barriers in position around the aircraft.

2        Place warning notices in the aircraft cockpit.

3        Ensure that Ground Safety Locks are fitted to all Landing Gears.

4        Ensure Wheel Chocks are fitted.

5        Ensure the Brakes are applied.

6        Ensure that the aircraft is balanced and stable.

7        Ensure that the aircraft is in the ‘Clean Flight Configuration’. (Flaps/Slats are housed)

8        Deactivate the relevant circuit breakers to ensure that there will be no movement of flight controls or the operation of other in-flight systems.  NB: As the aircraft is raised it moves from the ‘Ground Configuration’ to the ‘Flight Configuration’.

9        Fit Jacking Pads and Adaptors.

10      Position the jacks under the aircraft, just taking a little of the aircraft’s weight.

11      Remove Wheel Chocks.

12      Release the Brakes.

13      Ensure that all the passenger/crew doors, the emergency exits and the cargo doors are closed and locked or fully open and locked.

14      Remove access ladders and platforms.

15      Clear the area around the aircraft of all ground support and maintenance equipment and ensure that no other work is being carried out.

16      Operate the nose jack if necessary to ensure the aircraft is longitudinally stable.

17      Slowly operate the jacks at the same time to keep the aircraft level until the appropriate clearance is achieved between the main landing gear wheels and the ground.

18      Ensure that throughout the jacking operations the jack Safety Locking Collars are kept approximately 2.5 cms clear of the jack body.

19      On completion of all jack raising operations the aircraft should be levelled to the ‘datum position’, the jack Safety Locking Collars tightened and the aircraft made stable by the fitting of trestles or a safety stay.

Bottle Jack

The bottle jack consists of a hydraulic unit on a base-plate. 

These jacks may have single rams or double telescoping rams, and are made in various sizes.

A single acting pump is used to raise the jack ram.

A release valve is fitted, which when opened, allows fluid in the cylinder to return to the reservoir.  This allows the ram to descend.  Bottle jacks are used mainly for raising individual undercarriage legs in order to change wheels and brake units etc.

They may be used on their own or in conjunction with an adapter or swan-neck, which is attached to the undercarriage leg or boogie beam.

Types of Aircraft Jacks

Bipod Jack

The bi-pod jack consists of a hydraulic unit supported by two fixed legs and one adjustable leg.This jack is suitable for arc lifting.

The two fixed legs provide support on two opposite sides while the adjustable leg gives support on the third side.  The two fixed legs rest upon swiveling feet.  These legs support the load and may be tilted through a small angle, usually not exceeding 6°.  The adjustable leg is adjusted to steady the bipod legs as they move the jack body towards the vertical position during an arc lift.

The jacking point moves laterally as the aircraft is raised because the aircraft pivots about the wheels of the other undercarriage units

 

Tripod Jack

The tripod jack consists of a hydraulic unit supported by three fixed legs.This jack is suitable for vertical lifting.

It is not suitable for lifting where lateral movement of the jack develops during the jacking operation.  Lateral movement of the jack might occur when raising the aircraft to change a wheel after a tyre has deflated.

Quadrupod Jack

The quadropod jack consists of a hydraulic unit supported by two fixed legs and two adjustable legs.

This jack possesses all the advantages of the bipod, and consists of attaching an additional leg to the bipod jack.

The use of this additional leg gives increased stability to the jack.  It also forms the legs into a trestle, which can be rigidly locked when the jack is supporting an aircraft.

This jack can be used for an arc lift in a similar manner to the bipod jack.

Aircraft Jacks

There are many different types of aircraft jacks currently in use, however, they all fall into two groups, mechanical and hydraulic.

Mechanical Lifting Jacks

The mechanical jacks operate on a simple ‘screw jack’ principle, where a ratchet mechanism is used to raise the telescopic ram by use of a square thread.  These jacks are usually only used for raising small light aeroplanes, and some helicopters.

Hydraulic Lifting Jacks

The majority of aircraft lifting jacks operate on a hydraulic principle, which use the fact that oil will flow freely yet act as a solid, because it is in this context incompressible.  Another advantage of using the hydraulic principle, is that a relatively small piston pump can generate a lot of pressure to move the jack ram and aircraft upwards, with only a moderate effort on the part of the operator.