A B737-500 mechanic working the horizontal stabilizer hinge pin replacement job card mistakenly acti...

Attributes
ACN	778759
Time
Date	200803
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 0
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-500
Operating Under FAR Part	Part 121
Flight Phase	ground : maintenance
Person 1
Affiliation	company : air carrier
Function	maintenance : technician
Qualification	technician : airframe technician : powerplant
ASRS Report	778759
Events
Anomaly	aircraft equipment problem : critical maintenance problem : improper maintenance non adherence : published procedure
Independent Detector	other other : 1
Resolutory Action	none taken : detected after the fact
Consequence	other other
Factors
Maintenance	contributing factor : lighting performance deficiency : scheduled maintenance
Supplementary
Problem Areas	Environmental Factor Maintenance Human Performance Aircraft
Primary Problem	Maintenance Human Performance

Narrative:

While working the horizontal stabilizer hinge pin replacement airworthiness directive; I went to the cockpit to reset circuit breakers and run the stabilizer through full travel; as outlined on the airworthiness directive. The lighting in the cockpit was very dim. I reset a standby hydraulic circuit breaker thinking I saw stabilizer trim written above it. The standby hydraulic pump came on and drove the krueger flaps into the inboard thrust reverser cowls. The standby hydraulic pump kicked on because someone left the alternate flap switch in the arm position. The alternate flap switch is a red guarded switch and did not have a tag or streamer hanging from it as an alert that it was in the arm position. Callback conversation with reporter revealed the following information: reporter stated both engines had their inboard and outboard reverser cowls opened. The flap handle was set at the 40 degree position. He just never noticed the normally red-guarded 'arm' switch for the alternate flap drive was in the 'arm' mode in the dimly lit cockpit. The inboard reverser cowls were damaged.

Original NASA ASRS Text

Title: A B737-500 MECHANIC WORKING THE HORIZ STAB HINGE PIN REPLACEMENT JOB CARD MISTAKENLY ACTIVATES THE STANDBY HYD PUMP CIRCUIT BREAKER. PUMP CAME ON AND EXTENDED THE INBOARD LEADING EDGE KRUEGER FLAPS INTO THE OPENED THRUST REV COWLINGS.

Narrative: WHILE WORKING THE HORIZ STABILIZER HINGE PIN REPLACEMENT AIRWORTHINESS DIRECTIVE; I WENT TO THE COCKPIT TO RESET CIRCUIT BREAKERS AND RUN THE STABILIZER THROUGH FULL TRAVEL; AS OUTLINED ON THE AIRWORTHINESS DIRECTIVE. THE LIGHTING IN THE COCKPIT WAS VERY DIM. I RESET A STANDBY HYD CIRCUIT BREAKER THINKING I SAW STABILIZER TRIM WRITTEN ABOVE IT. THE STANDBY HYD PUMP CAME ON AND DROVE THE KRUEGER FLAPS INTO THE INBOARD THRUST REVERSER COWLS. THE STANDBY HYD PUMP KICKED ON BECAUSE SOMEONE LEFT THE ALTERNATE FLAP SWITCH IN THE ARM POS. THE ALTERNATE FLAP SWITCH IS A RED GUARDED SWITCH AND DID NOT HAVE A TAG OR STREAMER HANGING FROM IT AS AN ALERT THAT IT WAS IN THE ARM POS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED BOTH ENGINES HAD THEIR INBOARD AND OUTBOARD REVERSER COWLS OPENED. THE FLAP HANDLE WAS SET AT THE 40 DEGREE POSITION. HE JUST NEVER NOTICED THE NORMALLY RED-GUARDED 'ARM' SWITCH FOR THE ALTERNATE FLAP DRIVE WAS IN THE 'ARM' MODE IN THE DIMLY LIT COCKPIT. THE INBOARD REVERSER COWLS WERE DAMAGED.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

A B737-500 mechanic working the horizontal stabilizer hinge pin replacement job card mistakenly activates the standby hydraulic pump circuit breaker. Pump came on and extended the inboard leading edge krueger flaps into the opened thrust rev cowlings.