Aviation Investigation Report A98H0003
1.19.9 Restoration and Extraction of Non-volatile-memory Information
Many of the LRUs contained information within their NVM that could have been of use to the investigation, especially since the flight recorders stopped nearly six minutes prior to the time of impact. None of the LRUs of interest (FCCs, ADCs, etc.) were recovered intact. However, hundreds of loose circuit boards were recovered in various states of damage; many of the components were either partially or completely stripped from the circuit boards. Because the memory chips are not given any particular distinctive markings, identifying specific chips on circuit boards was very difficult and at times impossible. Honeywell, the manufacturer of the majority of the avionics used on the MD-11, provided technical assistance in identifying these NVM memory devices. It would aid accident investigations if the manufacturers of NVM devices could make them more distinguishable, either through colour coding or other markings.
Of the hundreds of circuit boards examined, only one FCC board still contained an EEPROM microcircuit. The device was damaged, predominately from corrosion and required highly specialized techniques to reconstruct it, including the FIBs technique previously discussed. Because of one stuck address, the memory was extracted in two phases. The second phase repaired the stuck address and the remaining half of the data was recovered.
The extracted data was passed to Honeywell for validation and interpretation. The data contained an ASCII representation of the contents of the maintenance memory EEPROM contained in the central processing unit 1A processor of one of the two FCCs installed on the aircraft. It is not known in which position the FCC was installed: left versus right or FCC-1 versus FCC-2.
Evaluation of the data showed three faults were logged on SR 111, on 3 September 1998 at 0124 UTC at an altitude of 11 328 feet and an airspeed of 321 knots. These were AOA-B TST (angle of attack-B test), AOA INV (angle of attack invalid) and FLAP POS INV (flap position invalid). All three faults are related to a loss of power; however, as the FCC position could not be determined, the faults cannot be isolated to a specific angle of attack vane or flap synchro.
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