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1.10. Aerodrome information.
Runway 24 at Ibiza Airport has a Landing Distance Available of 2,800
metres. The runway is 45 metres wide and is equipped with High Intensity
Runway Lighting, Centreline Lighting, a High Intensity Approach Lighting
System cat. I of 900 metres and Precision Approach Path Indicator System on
the left side of the runway, giving a 3° glidepath angle.
The runway has a 60 metre stopway (SWY) at the western end. The
overrun area (CWY), of 60 metres by 150 metres, consisted of levelled open
terrain. The area behind the SWY-CWY was almost level, slightly sloping to
the right down to a drainage trough, and it was covered by tall grass and sparse
wild scrub vegetation; then it sloped up at a higher angle and it was here where
the aircraft came to a rest. Some 350 metres beyond the end of the runway was
the airport boundary concrete and stone wall, which bordered onto a beach and
the Mediterranean sea.
1.11. Flight recorders.
1.11.1 Digital Flight Data Recorder (DFDR)
The aircraft was equipped with a Sundstrand Universal Flight Data
Recorder (UFDR), model 980-4100-AXUS, with a recording duration of 25
hours using magnetic tape. An initial replay was attempted using the facilities
and the standard interface unit connected to the UFDR. Although some data
was obtained, the data ended with the aircraft still travelling at a speed of 65
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kts and so did not cover the final period of the landing roll. Further attempts
were made to replay the recorder, but no further information was obtained.
The unit was then examined in Madrid at the airline workshops. The
tape enclosure was opened and the tape found to be damaged such that the unit
would not run. The supply and take up reels are driven by a peripheral belt. As
found, the peripheral belt was curled over the reel and the tape stack was
uneven. The tape path from the supply reel to the take up reel, over the record
heads, passes over a number of tape guides. At one of these tape guides, the
tape had actually become doubled over causing damage to the tape.
The tape was removed from the recorder and replayed on an ‘open reel’
system at AAIB in Farnborough, UK. Data covering the period of the landing
roll and up to when the aircraft was shutdown was recovered; however due to
the tape damage which had occurred during the first attempt to replay the
recorder, some areas of data could not be recovered.
The FDR does not run continuously when it is recording. It stores data
into one of two volatile memory stores, each holding approximately one second
of data. When one memory is full, the data flow is switched to the other store.
While data is being fed to this other store, the tape is rewound and the previous
second of recorded data is checked. A gap is left on the tape and the data from
the first store is written to the tape after said gap, and the first memory is
emptied. The whole ‘checkstroke’ operation takes much less than one second
to complete so that once the second store is full, data is switched back to the
first store, and the second store is written to the tape using the ‘checkstroke’
operation again. The procedure is then repeated. When power is lost from the
recorder the data held in volatile memory, which has not been recorded on the
tape, is lost.
During replay the FDR runs continuously and the most frequently
reported failure mode in this condition is tape ‘coning’, where the flat disk
appearance of a normal tape pack is distorted. When this occurs the tape
becomes misaligned with the heads and no signal is obtained from the tape. In
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this case the tape probably ‘coned’ during the initial replay by standard means,
and continuing to run the recorder caused the damage seen in the tape assembly
(see Appendix C).
This FDR had been fitted to the aircraft on 20 May 1998, the day prior
to the accident. A Solid State storage unit had been removed for a routine
readout. No faults were found with the FDR when it was sent for investigation
after the accident, and the recovery of all the data up to the loss of electrical
power indicates that the recorder had been serviceable.
The recording on FDR stopped 63 seconds after touchdown as the
engines were shutdown and electrical power was lost.
Data from the initial readout and the final ‘open reel’ replay were
combined to produce the final listing of the last 70 seconds of data.
The initial Autobrake LO selection was made at 23.55 UTC (52 minutes
and 28 seconds before touchdown), during the cruise at an altitude of 33,000 ft.
This parameter is sampled and recorded every 4 seconds by the FDR; the
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