Discuss the methods of protection against HIRF and the checks/ inspections which would be carried out after a fault was entered in the technical log.
High Intensity Radiated Field (HIRF) is produced by high energy systems located on the ground and occurs at all frequencies. It affects any electronic and digital systems on the aircraft, causing affected systems to operate erratically.
Aircraft and systems can be protected against HIRF by
proper shielding of cables,EMI filters, good bonding, electro static discharger. Proper termination of aircraft system connectors and sealing of LRUs conducting surface on windows, screening of cables.
If a fault had been entered in the technical log as HIRF I would make the aircraft safe in accordance with the Aircraft Maintenance Manual (AMM) and raise any other paper work required. I would attempt to isolate the fault, debrief the air crew, if necessary and confirm it is HIRF and not just a fault with the systems involved. The technical log could be consulted to establish if there is a pattern of previous similar faults. If HIRF appeared to be the cause I would check the serviceability of EMI filters, continuity check of shielding and bonding and carry out BITE (Built In Test Equipment) tests where possible to rectify the defect. And also check for the following:
- Detailed bonding resistance.
- Using loop resistance tester to measure the loop resistance/ impedance measurement.
- Disassemble the connector to detect corrosion.
- Arrange to reconfirm loop position within the limit. Carry out related system functional test.
Any work carried out would be recorded and signed as the job progressed. If any items were replaced crosscheck the EASA Form 1 or FAA 8130-3 for items airworthiness conformity and would be attached to paper work, part numbers GRN’s,serial numbers on and off would be recorded. CRS would be issued by a appropriately authorized engineer and a statement would be made in the technical log to monitor the systems affected on the next flights.
As any occurrence of HIRF is an incident this must be reported to the CAA through the Mandatory Occurrence Report (MOR) scheme. I would also report it to the organisation HIRF programme.