DAVID LEARMOUNT / LONDON
Swiss authorities have checked the Zurich radio navigation beacon used by the crashed Crossair BAE Systems Avro RJ100 and found that it was operating "within acceptable tolerances". Also, they say, there appears to have been nothing wrong with the aircraft, a statement which Crossair has tacitly accepted in suggesting that the RJ100 had suffered a "controlled flight into terrain" (CFIT) accident (Flight International, 4-10 December).
The Swiss civil aviation authority (OFAC) has since issued weather minima of 4,000m (13,000ft) visibility and a cloudbase 1,200ft (above ground level (AGL) on the approach for clearing the use of the VOR/DME (distance measuring equipment) letdown to runway 28. The visibility on the night of the accident was 3,500m in light snow, with the lowest cloud 600ft above airfield elevation and the main cloudbase at 1,500ft, according to the Swiss accident investigator BFU.
Since the 24 November accident, in which 21 passengers and three crew died when the aircraft hit the ground on the approach to runway 28, Crossair has announced that it is setting higher weather criteria for its flights than the published OFAC figures, requiring visibility to be 5,000m and cloudbase 1,500ft AGL.
On the night of the accident, an aircraft ahead of the Crossair flight had reported that the runway was in sight from 2.2nm (4km) from the Kloten VOR/DME beacon, which is located in the middle of the airport, not at the runway touchdown point. The precision approach path indicator (PAPI) lights beside the runway touchdown point are set for a 3.7° glideslope, steeper than the standard 3° because there is rising terrain under the runway 28 approach path. The cockpit voice recorder shows that an altimeter setting error is unlikely, because the pilots set and compared their altimeters on being given the pressure setting.
BFU says that the aircraft first hit trees at 1,784ft above sea level (368ft above runway elevation) at about 2nm from the runway threshold and slightly to the left of the runway extended centreline. At that point on a safe 3.7° slope the aircraft should normally have been at about 700ft above runway elevation and the crew should have had the runway lights in sight before reaching that point.
The published minimum descent height, below which a crew should not descend without the runway in sight, is 974ft above runway elevation, and this point should be reached at about 5km from the runway end. According to the BFU report there was no indication from either of the crew that they had the runway in sight when, just before impact, the pilots started a go-around procedure.
Source: Flight International
