On the night of April 26, 1994, China Air Lines flight 140 made its
final approach to Nagoya, Japan. The weather over Nagoya was perfect,
clear with light winds. The Airbus A300-600R was in top mechanical
condition and had just been certified. The European built airliner was
still very new in all aspects, having been added to the Taiwanese based
air carrier only a few months before.
As the airliner approached within feet of the runway it began to
lurch back into the air, nosing up quickly as if it did not want to
land. The pilot, an experienced flier, cursed as he fought with the
jet, trying to force it back onto the runway. However, each time he
pushed down to land, the jet bucked back into the air.
Three times the pilot fought with the controls. Each time the modern
airliner seemed to respond with a mind of its own, pulling up hard at
the last second. On the third nose up maneuver the airliner lost almost
all its speed. The Airbus hesitated for a moment, hanging motionless a
thousand feet in the air over the runway, and then with a shuddering
blast, crashed backwards onto the Nagoya airfield, killing all 231
aboard.
What happened to CAL flight 140? According to information gathered
by the flight data recorder, the pilot had placed the airliner into a
computerized “touch and go” mode that forced the aircraft to pull up and
away during landings. This maneuver is practiced by pilots, allowing
the airliner to gently skip off the runway and back into the air.
Unknowingly, the pilot overrode the computer by pushing the nose back
down to land but never turned the computer off. In response to each
landing attempt, the computer dutifully followed its preset program and
pulled the jet back up. The pilot, determined to land the aircraft,
engaged in a battle for control of the plane. The result was a classic
computer “loop.” Each time the pilot pushed the airliner down to land,
the computer obediently pulled the jet back up to go around. On the
third try the entire system, including the airliner, crashed.
Nor is the dramatic example of CAL flight 140 the only instance of
death by software. On Jan. 20, 1992, an Airbus A320 flown by Air Inter,
a regional French carrier, crashed while on approach to
Strasbourg-Entzheim airport. The crew, with over 12,000 hours of
combined flying experience, decided to set the airliner to descend by
computer control. They set the airliner to glide downward to the
airport at what they thought was a gentle “3.3” degree slope.
However, the pilots actually set the airliner to descend at a rate of
“3,300” feet per minute, a rate four times what they expected. The jet
with 96 persons on board slammed into the Alps at 2,620 feet, killing
87, including both pilots.
The investigation into the Air Inter crash led to some very
disturbing evidence uncovered by the French Transport Ministry. The
parent airline, Air Inter, did not give their pilots official
information on software technical problems reported on the A320. The
French carrier was under a financial strain at the time of the crash,
and was also locked in a labor struggle with the pilots union. The Air
Inter management decided not to release any data given to them by
aircraft manufacturers that could be used as bad press during the labor
dispute.
The Air Inter accident is not an isolated case. The events
surrounding the crash of a Comair Embraer EMB-120, caused by the
computer autopilot over compensating for icing conditions, have never
been fully addressed inside the United States airline system.
Comair flight 3272 crashed on Jan. 9, 1997, as it approached Detroit
Metro airport. Three crew members and 26 passengers died. The crash
brought to light the fact that the FAA was aware of the software problem
with the Embraer autopilot but chose not to inform pilots.
Moreover, death by software can strike any airline no matter how well
run. On Sept. 14, 1993, a Lufthansa Airbus A320-200 was landing in bad
weather at Warsaw airport, Poland. The pilots had been warned of
gusting cross winds, rain and possible wind shear conditions. In order
to compensate for the bad weather problems the crew added 20 knots of
speed to their landing approach and used a standard cross wind landing
technique, keeping the right wing low and landing first on the right
gear.
However, because of the gusting winds and heavy rains, the wheels
aquaplaned during the first nine seconds on the ground. The extra wind
and water combined to fool the Airbus computer, indicating the big jet
had not landed. The computer responded by disabling the aircraft
braking systems. With no brakes, the Lufthansa jet skidded off the end
of the Warsaw runway and struck a hill, killing the first officer, one
passenger, and injuring 45 others. The A320 was totally destroyed in
the crash.
The crash report that followed indicated the flight crew followed the
Airbus book on how to land the big jet in bad weather. Lufthansa, in
response to the crash, changed the procedures against the advice of
Airbus. No Lufthansa A320s have crashed since that change. Airbus, of
course, insists there is no problem in their control software.
The ability to program a computer to fly an aircraft is commonplace.
However, nations also make and defend artificial borders that are often
ignored by computers. For example, the shoot down of Korean airlines
KAL-007 by the former Soviet Union was due to a simple data entry error.
The pilot of the 747 jumbo jet accidentally set the airliner to fly
the most efficient course to its destination, a course that took it over
restricted Soviet airspace. The pilot that set the navigation computer
entered only two numbers out of sequence, guiding the doomed airliner
off course and into history.
It’s a digital world and computers control everything with clockwork
perfection. Pilots complain that they no longer fly airplanes because
of computer controls. One pilot recently quipped that customers should
“thank the programmer” for a smooth landing. Yet, faulty commercial
airline software and poor training can lead to an abrupt end of your
flight.
