PEI mentioned that important technical improvement not available in this CrossAir ALA-CFIT case: the newer
TCF (Terrain Clearance Floor) included in the later Enhanced GPWS.
PEI also mentioned "...
the accident was avoidable ... lacking precision approach ... instead of using a proven ILS approach...."
Before Enhanced GPWS, there were several cases of pilots flying an ILS approach, using a False Glideslope INDICATION, with NO Flags. One of these case happened at Zurich [sorry that Swiss Report must be in German]:
"... über den Unfall des Flugzeuges DC-9-32, ALITALIA, Flugnr. AZ 404, I-ATJA am Stadlerberg, Weiach/ZH, vom 14 November 1990 ..."
Alitalia 404 / 14Nov90 DC-9-32 I-ATJA , en route from Milan ... descended on ILS-approach to Zurich Rwy 14, impacted about 9.6 km from airport at night. All fatal, 40 passengers and six crew.
Even an ILS-approach (glideslope) proved unreliable sometimes. There were several presentations from investigators describing such descents on false glideslope, here's that Air New Zealand B767 /29July2000 at Apia:
Aero 21 - Erroneous Glidescope, and NZ's CAA offers their report "CAA Occurrence No. 00/2518"
About ten years ago BEA-guys made a presentation describing an MD80 CatIII coupled-approach to Paris, the crew flew final down to DH, then did a Missed' -- but the controllers noticed their position as still several miles out on final [good AAR, in English, but I can't locate the report].
Enhanced Ground Proximity Warning Systems Near Miss
In February 1999, an Air France Boeing 777 was approaching runway 10 at Rio de Ja-neiro’s Galeao International Airport. The flight was headed in an easterly direction thus blinding the pilots by the early morning sun. In addition, the runway itself was shrouded in mist. The pilots however continued their approach; relying on the Instrument Landing System (ILS), that provides the proper glide slope down to the runway.
Unknown to the flight crew, the Brazilian technicians were servicing the ILS transmitter. Following a false signal sent by the airport transmitter, the jet was descending toward a hill 4.8 kilometers short of the runway. Bertrand de Courville, Air France’s manager of flight safety, said that at the last moment the descending jet broke out of the mists.
The pilots, expecting to see the runway, were startled to see the hill. At the same moment, the jet’s Enhanced GPWS displayed the hilltop in red and issued an alert, “Terrain, Terrain. Pull up, Pull up.”
“The pilots leveled off,” missing the hill by about 98 meters, Mr. De Courville says. The jet then landed safely. Although the pilots had spotted the hill, “there were few visual cues, and the enhanced GPWS was very helpful” in confirming the danger ahead, enabling the pilots to save the plane.