OT: Jet crash blamed on wrong repair

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January 9 2000 BRITAIN

Jet crash blamed on wrong repair

HUMAN error may have compounded a minor fault leading to last month's crash of the Korean Air cargo plane at Stansted, it has emerged, writes Stephen Bevan.

Experts who have analysed the investigators' report of the accident on December 22, in which all four of the crew died, say mechanics may have unwittingly repaired the wrong piece of air navigation equipment.

A problem with the captain's attitude director indicator (ADI), which tells the crew whether the aircraft is level, climbing or descending, was reported by the Boeing 747's previous crew. So the ground engineers repaired it. However, an airline technical director said the fault really lay with the computer feeding the ADI, the inertial navigation unit.

An interim accident report revealed a vital piece of navigation equipment had failed before the crash. The flight engineer appears to have identified the problem after take-off, but the captain may have refused to believe his instruments were at fault and flew his aircraft into the ground, said the director.

-- Homer Beanfang (Bats@inbellfry.com), January 12, 2000


Believing (without question) what a machine tells you is not a best idea...

-- Mad Monk (madmonk@hawaiian.net), January 12, 2000.

Remember the admonishment that "planes will not fall out of the sky?"

-- charlie in houston (cml@workmail.com), January 12, 2000.

The KAL 747 involved in this crash likely used an analog nav computer rather than a fully digital one. The fact that the cockpit displays were ADI's (Attitude Director Indicators) points out that this was no "glass cockpit", digital aircraft. And analog systems are Y2K immune, being only "transistorized" or "solid-state" systems.

This would put the failure into the realm of a failed IMU (Inertial Measurement Unit), the sensors used to feed the ADI with pitch, roll and yaw information. IMU's are usually gyroscopes packaged with their associated signal drive electronics.

From my experience, IMU failures are a very common occurence. And they are one that flight crews should be properly trained to recognize and cope with. That's why on the flight instrument panel there is a back-up attitude indicator (AI) which the pilots should normally check for agreement with his primary ADI.


-- Wildweasel (vtmldm@epix.net), January 12, 2000.

The ultimate backup is "Needle, ball and airspeed". Literally every plane that flys has these, few pilots are competent to fly by these ancient gauges. They put so much trust in the modern HSI's and glass gizmos, they refuse to accept info from any other source (even if there is evidence the gizmo may be in error).

It ain't pretty, but you can control an aircraft with only the turn indicator (needle), the ball (skid indicator) and the airspeed indicator. About $500 total for new parts. And they are absolutely Y2K OK !

-- IFR (Beenthere@done.that), January 12, 2000.

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