A B737-700 returned to the gate after a failed solenoid in the a system engine driven hydraulic pump...

Attributes
ACN	951970
Time
Date	201106
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Taxi
Flight Plan	IFR
Component
Aircraft Component	Hydraulic System Pump
Person 1
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 303
Person 2
Function	First Officer
Experience	Flight Crew Last 90 Days 220
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy

Narrative:

During engine start the first officer placed the number 1 engine start switch to start and; shortly thereafter; the tow bar broke. Crew checked the a pump off; but the [low pressure] light was out and 3;000 psi was showing on the gauge when it should have been zero. The engine start was aborted and the speedbrake was deployed to bleed off pressure. Aircraft returned to the gate and maintenance was notified. Maintenance described the problem as a hydraulic engine driven pump solenoid failure causing the system to pressurize when not commanded. Maintenance replaced the solenoid and flight continued.

Original NASA ASRS Text

Title: A B737-700 returned to the gate after a failed solenoid in the A System engine driven hydraulic pump switch allowed the system to be pressurized during engine start which resulted in a broken tow bar.

Narrative: During engine start the First Officer placed the number 1 engine start switch to start and; shortly thereafter; the tow bar broke. Crew checked the A pump off; but the [low pressure] light was out and 3;000 PSI was showing on the gauge when it should have been zero. The engine start was aborted and the speedbrake was deployed to bleed off pressure. Aircraft returned to the gate and Maintenance was notified. Maintenance described the problem as a hydraulic engine driven pump solenoid failure causing the system to pressurize when not commanded. Maintenance replaced the solenoid and flight continued.

Data retrieved from NASA's ASRS site as of April 2012 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 B737-700 returned to the gate after a failed solenoid in the a system engine driven hydraulic pump switch allowed the system to be pressurized during engine start which resulted in a broken tow bar.