MD80 crew broke the steering bypass pushing throttle forward during aircraft pushback.

Attributes
ACN	551312
Time
Date	200206
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : dfw.airport
State Reference	TX
Altitude	agl single value : 0
Environment
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Flight Phase	ground : pushback
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	551312
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : less severe non adherence : company policies non adherence : far non adherence : published procedure other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : egt, n2 rpm other flight crewa other flight crewb other other : 3
Resolutory Action	none taken : detected after the fact other
Consequence	other other other
Factors
Maintenance	performance deficiency : repair
Supplementary
Problem Areas	Company Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

Broke steering bypass during pushback. Aircraft had no APU, therefore, had to start both engines at gate for pushback. During pushback, noticed that the left engine was between 450-460 degrees and N2 was only at 49%. Turned left pack off and advanced left throttle about 1/2 knob width -- expecting to achieve approximately 55% N2. Egt remained at 460 degrees, so throttle was advanced to just less than 1 knob width. Noticed that the tug driver seemed to be more aft than normal, but we were still moving backwards. Checked left egt and looked outside and noticed that the aircraft was moving forward, but tug was not. Slammed on brakes to top movement. After aircraft topped, there was a pop and the tiller centered. Somewhere in the stop maneuver, suspect when we bobbed forward as aircraft stopped, left throttle was advanced to approximately 2 knob widths above right throttle. Damage was done to steering mechanism. Changed planes after being towed to gate and continued trip.

Original NASA ASRS Text

Title: MD80 CREW BROKE THE STEERING BYPASS PUSHING THROTTLE FORWARD DURING ACFT PUSHBACK.

Narrative: BROKE STEERING BYPASS DURING PUSHBACK. ACFT HAD NO APU, THEREFORE, HAD TO START BOTH ENGS AT GATE FOR PUSHBACK. DURING PUSHBACK, NOTICED THAT THE L ENG WAS BTWN 450-460 DEGS AND N2 WAS ONLY AT 49%. TURNED L PACK OFF AND ADVANCED L THROTTLE ABOUT 1/2 KNOB WIDTH -- EXPECTING TO ACHIEVE APPROX 55% N2. EGT REMAINED AT 460 DEGS, SO THROTTLE WAS ADVANCED TO JUST LESS THAN 1 KNOB WIDTH. NOTICED THAT THE TUG DRIVER SEEMED TO BE MORE AFT THAN NORMAL, BUT WE WERE STILL MOVING BACKWARDS. CHKED L EGT AND LOOKED OUTSIDE AND NOTICED THAT THE ACFT WAS MOVING FORWARD, BUT TUG WAS NOT. SLAMMED ON BRAKES TO TOP MOVEMENT. AFTER ACFT TOPPED, THERE WAS A POP AND THE TILLER CTRED. SOMEWHERE IN THE STOP MANEUVER, SUSPECT WHEN WE BOBBED FORWARD AS ACFT STOPPED, L THROTTLE WAS ADVANCED TO APPROX 2 KNOB WIDTHS ABOVE R THROTTLE. DAMAGE WAS DONE TO STEERING MECHANISM. CHANGED PLANES AFTER BEING TOWED TO GATE AND CONTINUED TRIP.

Data retrieved from NASA's ASRS site as of July 2007 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.