Service difficulty report · Sensor · Boeing 747422

Difficulty date
December 1, 2004
Submitted
December 7, 2004
Operation
Air carrier
Aircraft
N197UA
Make and model
Boeing 747422
Aircraft serial
26901
Aircraft time
28,592 hours, 3,630 cycles
Engine
Pwa PW4056
Part
Sensor
Condition
Malfunctioned
Location
Aoa
Stage of operation
NR
How discovered
9
Nature of condition
O
Precautionary procedure
O

As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.

What was found

ALTIMETER SPLIT 240-250 FT WITH RT SIDE READ LOW. THE RT AOA PROBE IS SUSPECTED TO BE PROVIDING ERRONEOUS INDICATIONS TO THE ADC AT HIGH SPEEDS (0.8 - 0.9 MACH). THE AIR DATA COMPUTER TAKES AOA INPUTS TO MAKE CORRECTIONS TO THE PITOT-STATIC PRESSURES. DURING HIGH SPEEDS, THE INCORRECT AOA INDICATIONS WERE CAUSING ERRONEOUS CORRECTIONS TO BE APPLIED BY THE AIR DATA COMPUTER, THEREBY RESULTING IN SPLIT ALTIMETER INDICATIONS BETWEEN THE CAPTAINS AND FIRST OFFICERS SIDE. REPLACEMENT OF THE FIRST OFFICERS ANGLE-OF-ATTACK PROBE RECTIFIED THE PROBLEM.