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ATA 07

Lifting and Shoring.

This chapter will tell you how to safely lift or in case of emergency shore an airplane.

When do you need to lift an airplane ?

Here there are two possibilities :

1. For main or nose gear replacement. Or parts of the landing gear.
2. For main gear and/or nose gear retraction test.

Possibility number 1:

In case of replacing only a part of the landing gear it’s only the landing gear its self that gets lifted. In case of a bogie it’s only one side that gets lifted. The front or the rear part of the bogie beam.

For those who don’t now what a bogie beam is : you can imagine it as a large “H” that pivots at the middle of the “H” and with one wheel on each leg end. So a total of four wheels on the bogie beam. In some cases it’s even possible that there are more wheels mounted, like for incense the Boeing 777, he haze a total of 6 wheels on each bogie beam. But more about this in chapter 32 “landing gear”.

NOTE : only ONE wheel assy cane be replaced at the same time, so the opposite wheel assy has to be replaced after or before. In case that one wheel assy comes to carry the weight that supposed to be carried by two, that one wheel becomes overstressed and therefore also haze to be replaced, for instance by lift jack malfunction.

Quote: ”I lifted the front of the left hand bogie beam to be able to replace wheel assy number 2. After  the removal of this wheel I noticed that the number 1 wheel was back on the ground, after some fast investigation of the landing gear lifting jack I found that the jack had an internal leak causing the jack to lower slowly without me noticing it what so ever!
I lifted the landing gear again and installed the wheel assy I was busy with replacing. Then swapped the jack with an other one and now I could start again, this time to replace the number 1 wheel because it was overstressed, it had got to much weight on it. Damned jack!! Now I had to replace two wheels for the price of one!!”

This little story is taken out of my personal history as an airplane mechanic.

Possibility number 2:

In case of number 2 it’s the complete airplane or only the nose that gets lifted. This is sometimes necessary to be able to test the retraction and/or extension of the landing gear.
In case a sub-system of the landing gear has a malfunction it will also be tested this way.

Every airplane has at leased 3 reinforced spots able to support the weight of the airplane.
These “reinforced spot” are called “jacking points”.
Most of the time there are 2 jack point at the wings (one at each wing!) the location of the third jack point depends where the “centre of gravity” is located. This is for every airplane type different. But what is the “centre of gravity”? Well, this is the point that in relation to the weight of the airplane lies in the centre. So towards the forward of this point or to the back the weight will be the same. The same for the wingspan (from wingtip to opposite wingtip).
So for example : a Boeing 727 Centre of Gravity or “CG” leis towards the back, because of the fact of his three engine mounted at the tail section while by a Boeing 737 the CG leis more towards the front because this aircraft has two engine mounted on his wings by means of pylons. Causing the engines to stick out  far beyond the front of the wing. So the third jack point with the 727 is….correct, at the back. While with the 737 the third jack point is located at the front of the wings.

During the lifting of the airplane it’s advisable to distribute the total fuel on board equally in both wings. Once the lifting is started it’s at most importance that the airplane is kept level horizontally in two directions. Nose-to-tail and wings leveled. This to prevent any damage to the wings, fuselage or any other part of the airplane during lifting or lowering back on the ground.

Once the airplane is lifted there’s a fourth jack positioned just to stabilize the airplane during retraction and extension of the landing gear, because moving the landing gear up and down creates a lot of shaking of the aircraft while he is on his jacks, scary sight belief you me! Going back to the previously mentioned B727 the fourth jack is positioned at the front, on the B737 it’s at the back. The systems that are energized automatically from the moment the plane loses contact with the ground are normally all deactivated to prevent any damage.

Damage? 

For example: pitot probe heating is only necessary in flight so during retraction test this system is deactivated.

HOW? Actually just by pulling the plug on the whole pitot heating system!
WHY?  Because inside the hangar there's no airflow, and on the ground it doesn’t frieze minus 56, so if the heating would stay on, the pitot probes heating element would burn itself. With replacement of the pitot probes as a result. And this is only one of many systems that go active automatically from the moment the landing gear goes of the ground. This is done to help the flight crew, so they don't have to think about it and so, they can't forget to put it on. In case you are wondering why pitot heating is so important, go to ATA 30, Ice and Rain protection.

So you see that lifting a large airplane isn’t as simple as lifting a car or something. Because only an airplane needs to have ”ground sensing”, to automatically turn several systems on at lift-off.

Lifting equipment.

The lifting equipment, also called “JACKS”, are made in different sizes for each airplane there are a set of particular jacks. The jacks used for a A300 can’t be used for a Boeing 757 or a B727 for instance. So each airplane has his own set of jacks.

These jacks are manually and/or pneumatically operational. When the jacks are positioned under need there jacking point, there can be pumped manually or pneumatically until the jack is against his jacking point. The pneumatic system consist of a pneumatic motor driving a hydraulic pump which in turn pumps hydraulic fluid into the cylinder, lifting the piston inside upwards and so lifting the airplane itself. The lifting is done pneumatically. I have done it several times manually, and I cane state that the lifting of an Airbus A300, for example, by hand operating the jacks is a good work-out! When the plane is OFF the ground your ON the ground asking for water !!!

For info : Airbus A300B4, Operating empty 88,500kg (195,109lb), max takeoff 165,000kg (363,760lb). So far lifting an airplane.

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