Originally Posted by
Chris Scott
The last time frame whose data is totally uncorrupted is TGEN 334.0, and is treated, IIRC, as t-zero in the reports.
During TGEN 335.0, the data start to unhinge. That, following what appear to be uncorrupted signs of the initial impact, is particularly noticeable in the 4 sequential values of x and y accelerations (longitudinal and lateral respectively), and the 8 values of z (normal) acceleration presented in Tome 3. In Tome 1, the single sample of GS glitches to 648 kt.
Just to be clear, this should not be seen as anything particularly untoward in terms of process. As it turned out, the Loral-branded F800 DFDRs fitted to early A320s had issues with data corruption when subjected to shocks over a given threshold:
G-KMAM Incident
The DFDR was a Loral F800. This type of recorder has been found to give poor performance on the A320, and the investigators discovered that the DFDRs on all four of Excalibur's A320s had a history of problems, including random track changing, incorrect Built-In Test Equipment (BITE) indications, and corruption of data (AAIB 2/95 Sections 1.11 and 2.11). The track changing and BITE problems were cured by the replacement of a certain Electrically Erasable Programmable Read Only Memory (EEPROM) unit, a modification which Loral made mandatory only in response to considerable pressure from industry and regulatory agencies.
The data corruption appeared to be due to vibration. The anti-vibration tray on the A320 had not been tested to the requirements of Radio Technical Commission for Aeronautics (RTCA) document DO-160 "Environmental Conditions and Test Procedures for Airborne Equipment". Trials after the incident showed that the recording quality was improved by mounting the DFDR on a tray conforming to the DO-160 standard.
(AAIB 2/95 specifies the DFDR as "Loral F800". The DFDR on F-GFKC which crashed at Habsheim in 1988 was referred to as a "Fairchild F800" and that on F-GGED which crashed at Strasbourg in 1992 as a "LORAL-Fairchild F800" in the appropriate reports. Presumably these are all references to the same make and model of DFDR.)
Since 1989, Airbus Industrie have used a different make of recorder for all test and certification flights. It is stated (AAIB 2/95 Section 1.11, p 17) that the Loral recorder is fitted only on delivery to the customer. Precisely what the status of the airworthiness certificate is following this modification is not clear!
A320 Spoiler Disconnection
Investigation of this revealed that this was a common problem and that although Airbus had made a number of approaches to Loral regarding the unit, the situation had not improved.