Cockpit Confusion Preceded Airliner Crash in Guam
Confusion reigned in the cockpit of Korean Air Flight 801 in August as the jumbo jet sank steadily below the safe approach path before crashing into a hillside while attempting to land at an airport in Guam.
The confusion was so complete that National Transportation Safety Board investigators are having difficulty figuring out exactly what happened in the cockpit--and why--during the final moments before the Boeing 747 crashed, broke up and burst into flames, killing 228 of the 254 on board.
Transcripts of cockpit voice recordings recovered from the wreckage showed Tuesday that much of this confusion centered on a component of the instrument landing system called a glide slope. It’s a radio beam that tells the cockpit crew whether the plane is descending at the correct angle for a landing.
Flight 801’s crew had been told repeatedly that the glide slope was inoperable, which meant the crew should have used a commonly employed alternative system to make what investigative sources say should have been a routine landing.
However, the pilot, co-pilot and flight engineer aboard Flight 801 never seemed to get this clear, questioning one another several times about the glide slope, which had been turned off for repairs.
Korean Air had first been informed about the shutdown through an official bulletin issued by the Federal Aviation Administration, and the transcripts released Tuesday indicate that as the plane flew south from Seoul before dawn on Aug 6, the captain, Yong-Chul Park, speaking in Korean, told his crew that “the localizer glide slope is out.”
Reinforcing this message about half an hour later, an air traffic controller in Guam radioed the plane--in English--that the glide slope was “unusable.”
The controller, Kurt Mayo, testified Tuesday during the first day of NTSB hearings on the crash that when the plane responded with a “Roger,” he assumed that Flight 801 “had received and understood my transmission in its entirety.”
Because of language differences or some other problem, Mayo was wrong.
“Is the glide slope working?” the flight engineer, Suk-Hoon Nam, asked Park moments later.
“Yes, yes, it’s working” Park replied, flatly contradicting his earlier briefing to the crew.
“Ah, so . . . " Nam said.
“Check the glide slope . . . " someone in the cockpit said.
“Why is it working?” someone asked.
“Glide slope is incorrect,” someone said.
Veteran pilots familiar with instrument landing systems say a quick glance at the cockpit’s glide slope indicator should have confirmed immediately that the system was off. When the radio beam is shut down, a needle showing the plane’s position on the glide slope should disappear from view and a small red “flag” should pop up, showing that the system is inoperable.
On the other hand, the NTSB’s Greg Feith, who is heading up the probe, said Tuesday that his investigators are looking into the possibility that “spurious radiation” from some other source might have generated some sort of misleading readout on the glide slope indicator.
The transcript shows that as the plane continued to descend, Park told his crew that “since today’s glide slope is not good,” they should adopt the stepped-down approach path utilized when the system is out of service.
That might have been fine, but the plane already was beginning to drop well below the minimum safe altitudes for each of those steps.
Even though an on-board radar system had begun announcing through a cockpit loudspeaker that the plane was dropping dangerously low, Park, Kam and the co-pilot, Kyung-Ho Song, proceeded calmly though a routine landing check list, seemingly oblivious to the impending disaster.
Further adding to the confusion, Park suddenly asked: “Isn’t the glide slope working?”
No one answered him, and the plane continued to drop. As Flight 801 descended--and the loudspeaker continued to bark out critically low altitude readings--the crew members went on with the check list.
Finally, with the plane only about 500 feet above the ground--well below the highest peaks on Guam and roughly 1,000 feet below where it should have been--someone said: “stabilize, stabilize,” apparently suggesting that the descent be halted.
“Oh, yes,” Park replied.
Nonetheless, a maddening 18 seconds went by--with Kam still ticking off the items on the landing check list--before Song took the initiative and suggested a “missed approach” procedure, which calls for the plane to climb out and circle for another landing attempt.
Investigators have suggested privately that a traditional Korean deference to Park’s command authority may have critically delayed Song’s decision to act.
“Go around,” Nam said, seconding Song’s suggestion.
“Go around,” Park concurred.
A flight data recorder recovered from the debris showed that the pilots began to rev the engines and pull up the nose, but it was too late. “100 [feet],” the loudspeaker barked. “50 . . . 40 . . . 30 . . . 20. . . . “
A split second later, there was the sound of impact. Three seconds after that, there were some groans. Then silence.