From Select Committee on Chinook ZD 576:
"The aircraft was fitted with a Racal Avionics "SuperTANS" Tactical Area Navigation System providing navigation information from two independent sources. The system enables a number of way points to be fed into it before a flight. When flying from the point of departure to the first way point the screen[20] shows bearing, distance and "time to go" from the aircraft's current position to the way point. When the pilot alters the system from the first way point to the second, the distance and bearing of the former are replaced on the screen by those of the latter and so on as way points are progressively changed. Racal confirmed that the system was performing perfectly at the time of loss of power and extracted from its memory the information that way point B had been selected when way point A was 0.81 nautical miles distant, bearing 018°. The distance from the way point change to the point of impact was 0.95 nautical miles. The system gave no information as to height or time at the way point change but had recorded that at approximately 15-18 seconds before power down the aircraft was at a height of 468 feet ± 50 feet (Board report para 49). The manufacturers have told us that "18 seconds is likely to be a better estimate".[21] The TANS had also recorded that the height above sea level at impact was 665 ft[22], whereas in fact it was 810 ft. The investigating board noted this discrepancy (para 49); they considered it probably due to "the mechanics of the crash and the developing fireball", but we know of no evidence to support this. The TANS is not intended to act as a Flight Recorder or what is colloquially known as a Black Box, and the information referred to above was achieved by a somewhat complicated and ingenious method of extraction employed by Racal."