US investigators yesterday found that a computer warning system at Guam airport which could have prevented last week's crash of Korean Air Flight 801 was out of service at the time, an official said.
Meanwhile a Taiwanese plane crashed yesterday into a hilltop about one kilometre from an airport where it was to land and exploded on an island near China's coast, killing all 16 passengers and crew, officials said.
In the Guam crash investigation the National Transportation Safety Board (NTSB) found out that a radar minimum safe altitude warning (MSAW) system operated by the approach controller was not working apparently due to a software failure, a NTSB spokesman, Mr George Black, said.
"This is not the cause [of the crash], but it could have made the difference," he told a news conference.
The Guam airport authority had acknowledged earlier that a glide scope system which provides an electronic beam to guide the descent of a landing plane was removed for maintenance about a month before Wednesday's crash which killed 225 people.
The Boeing 747-300 plowed into a ravine five kilometres short of the Guam airport during a thunderstorm in the early hours of Wednesday.
Mr Black said the two warning systems were "redundancy" alerts designed to complement cockpit instruments that warn the pilots if they are flying too low as they approach an airport.
It does not relieve the pilots of their responsibility for maintaining a safe flight altitude with the use of their on-board warning systems, such as radio navigation instruments and radar, he added.
Mr Black said it was "too early to determine" whether these cockpit systems were operating normally at the time of the crash, or whether airports which lacked both these warning systems on the ground could be considered safe.
The investigators earlier said the plane's starboard wing had apparently hit a ridge.
"Both the glide scope and the MSAW are operated by the Federal Aviation Administration," Mr Black said. An unidentified witness, whom he described as an "approach controller," had informed the investigators that the MSAW was down due to "software error" after the authorities made adjustments "to reduce the number of false alerts" generated by the previous version of the software.
He said they had not determined how long the MSAW system had been down. The MSAW alerts the approach controller that an airplane on a landing manoeuvre is flying too low for comfort. The controller in turn alerts the pilot of this fact, Mr Black said.
In yesterday's crash most of the passengers were civilians, including five members of one family. Matsu island, just off the coast of China's Fujian province, is a front-line military garrison for Taiwan's nationalist forces.
Airport officials said the Formosa Airlines Dornier 228 ploughed into the 290metre Pishan hill, about a kilometre from the island's airport, as it approached for landing. A local government official, Mr Liu Li-chun, said the plane would have cleared the hill had it been five metres higher.
"The explosion was so loud that passengers waiting at the airport could hear it," he said. The Matsu town chief, Mr Wang Ssuchien, speaking to local television, added: "I saw the plane hit the top of trees and a water tower of a military unit before it crashed and exploded." Rescuers dragged a female survivor from the burning wreckage, but she died from severe burns and multiple fractures just after arriving at hospital.