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Pre-Flight Test Unit

Technical Information

Catalogue No: C0542
Category: Maintenance Systems
Object Type: Test Equipment
Object Name: Pre-Flight Test Unit
Part No: 74D3213-A-1
Serial No: 001/67
Manufacturer: Elliott Bros (London) Ltd
Division: Flight Controls [FCD]
Platform(s): Harrier
Year of Manufacture: 1967
Width (mm):
Height (mm):
Depth (mm):
Weight (g):
Location: Rack RAA07 [Main Store]

Pre-Flight Test Unit
Type No. 74D3213-A-1
Ref. No.
Ser. No. 001/67


Very little is known about this item, but it is very early in the Harrier programme as the first Harrier GR1 production order was only received in early 1967. This suggests that the equipment was already developed for the previous Kestrel or P1127 projects. The construction suggests that it is located on the Harrier, probably in the equipment bay. It was used to check out the aircraft systems prior to flight by monitoring the Built in Test Equipment in the avionics and commanding test functions. The given dimensions exclude the ten 300mm long cables. The hinged front panel cover does not conceal any further controls but allows maintenance access to the front of the test set.

BITE (Built-In Test Equipment) is a troubleshooting system installed in modern jet aircraft. BITE monitors the engine and airframe systems and when a fault is found, isolates it and provides the maintenance personnel with a code that identifies the LRU, or line replaceable unit, that contains the fault.

The LRU will contain both initiated and automatic test sequences which are small programs designed to test specific functions

A computer will have tests run at start-up which are only run at that time as they would interfere with normal operation. Once the computer has stabilised cyclic tests (also called operation test) will be carried out.They are carried out permanently, because they do not disturb normal operation. Examples: Watchdog test (i.e. CPU reset). RAM test.
System tests are available to the maintenance staff, for troubleshooting purposes. These tests are similar to ground power-up tests, but more complete. Examples: Tests performed after the replacement of an LRU.
Specific tests are available only to specific systems.
They are performed to generate stimuli to other devices, such as actuators or valves.
They have major effect on aircraft (such as automatic moving of flaps etc.) They are performed only on ground by maintenance staff.


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