On 28 Jun 1999, a British Airways jet and a Korean Air jet nearly collided
when the latter's TCAS unit told the pilot to climb. The Korean Air plane
was 2000 feet below the British Airways plane; however, the pilot was told
that it was in fact 400 feet *above* it. That's too close, so the pilot was
advised to climb. And that, of course, almost induced a collision.
Part of the problem was with a circuit that sends the plane's altitude to
the TCAS system and to the transponder. The circuit uses an 11-bit code
over a parallel connection; a single-bit error, which occured in testing,
would correspond to a 2400 foot difference in altitude -- precisely the
error here. (The article also notes that on a previous flight, the crew of
this plane was advised that their transponder was giving the wrong
altitude.)
The British Airways jet, though, had a TCAS system that noticed an
instantaneous jump in the altitude of the other plane. Since that's
impossible, the bad readings were properly ignored, which in turn meant that
there was no warning to the crew. When the TCAS system finally did detect
that the other plane was climbing towards it, it could only say tell the
pilots to dive, since the other plane was climbing. But that, according to
the article, was precisely the wrong thing to do.
The Korean Airways jet's TCAS system does include a comparator circuit to
verify the altitude reading. Due to a wiring problem, however, that circuit
was silently disabled; there is no warning to either pilots or mechanics of
this condition. And the faulty altitude reading occurred when engineers
left the air-data computer "on for a long time and added extra electrical
power".
13 JAN 2000
The Korean government ordered Korean Air to ground nine of its older-model Boeing 747s for a safety investigation. One of these Boeing 747 cargo jets landed in Malaysia with a 1-meter hole in its fuselage, caused by a wing flap that came loose.
Date: 06 AUG 1997
Type: Boeing 747-3B5
Operator: Korean Air
Registration: HL7468
Crew: Fatalities: 22 / Occupants: 23
Passengers: Fatalities: 206 / Occupants: 231
Total: Fatalities: 228 / Occupants: 254
Airplane damage: Written off
Location: near Guam-Agana International Airport (GUM) (Guam)
Phase: Approach (APR)
Nature: International Scheduled Passenger
Departure airport: Seoul-Gimpo (Kimpo) International Airport (SEL/RKSS), South Korea
Destination airport: Guam-A.B. Won Pat International Airport (GUM/PGUM), Guam
Flightnumber: 801
Narrative:
The aircraft was conducting a night-time approach to Guam runway 06L. Because of the unavailability of the ILS glide slope system (due to upgrading of the system), a VOR/DME approach was flown.
Flight 801 had descended 800 feet below the prescribed altitude, struck the 709 feet Nimitz Hill at a height of 650 feet and crashed in a jungle valley, breaking up and bursting into flames. The aircraft ended up at a height of 560 feet, 250m from the UNZ VORTAC (located on the top of Nimitz Hill).
It was established a.o. that the software fix for the Minimum Safe Altitude Warning (MSAW) system at Agana Center Radar Approach Control (CERAP) had rendered the program useless. A software patch had been installed since there had been complaints of the high rate of false MSAW alarms at Guam. This made KAL801's descent below MDA go undetected at the Agana CERAP.
PROBABLE CAUSE: "The captain's failure to adequately brief and execute the nonprecision approach and the first officer's and flight engineer's failure to effectively monitor and cross-check the captain's execution of the approach. Contributing to these failures were the captain's fatigue and Korean Air's inadequate flight crew training. Contributing to the accident was the Federal Aviation Administration's intentional inhibition of the minimum safe altitude warning system and the agency's failure to adequately to manage the system."
Martin: I suspect things have change a little in the almost 20 years from then to now...........maybe, maybe not. We use Korean regularly with excellent service and thus far......well, we are still here.
That's OK nooga,
I was just looking on Google Earth and on the approach to 06 at Guam there is a purple spot highlighting where the aircraft went down, so, always look on the bright side, you might have your own purple spot on Google Earth one day.
Yes jetmba,
They do have such, otherwise, floating vessels on Google Earth also, if you have Google Earth then search for 'Kwajalein', zoom out a little and look just offshore of the nearest piece of land to the north west, another purple spot.