Delay in landing occurs after loss of a portion of ATR-42's hydraulic system is experienced.

Attributes
ACN	288216
Time
Date	199411
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : lft
State Reference	LA
Altitude	msl bound lower : 1600 msl bound upper : 1600
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tower : lft artcc : zdv
Operator	common carrier : air carrier
Make Model Name	ATR 42
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : instrument pilot : atp
Experience	flight time last 90 days : 260 flight time total : 8030 flight time type : 3200
ASRS Report	288216
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 120 flight time total : 2500 flight time type : 120
ASRS Report	288358
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Upon configuring aircraft for landing momentary power loss occurred when main landing gear lowered. Blue hydraulic system air conditioning 'wild pwred' hydraulic pump failed. Entered holding pattern over field, completed emergency checklist, brought backup system on line and notified flight attendant. Normal landing initiated. Captain made landing. Made use of cockpit resource technicians and emergency training. Callback conversation with reporter revealed the following information: reporter revealed that the post flight inspection showed a failure of the left side hydraulic pump. This pump malfunctioned during the lowering of the landing gear. Since it is AC pwred by the 'AC wild system' it overloaded the AC wild generator and blew its circuit breakers. The cross tie bus relay that is supposed to close at this point to power the hydraulic system from the right (green) side failed to operate, necessitating the use of the checklist to get the hydraulic and electrical power back into the correct system. The 'wild' AC generator is only pwring the hydraulic pumps when the propellers are turning, pwred through the propeller reduction gear box. There are 2 other generators that run off the engines but they do not power the AC wild system pumps. This aircraft does not have an APU, it has a propeller brake on the right engine and therefore can run the right engine as an APU while 'braking' the propeller. Reporter felt that this was an odd happening and had not had any prior experiences like this in the ATR-42.

Original NASA ASRS Text

Title: DELAY IN LNDG OCCURS AFTER LOSS OF A PORTION OF ATR-42'S HYD SYS IS EXPERIENCED.

Narrative: UPON CONFIGURING ACFT FOR LNDG MOMENTARY PWR LOSS OCCURRED WHEN MAIN LNDG GEAR LOWERED. BLUE HYD SYS AIR CONDITIONING 'WILD PWRED' HYD PUMP FAILED. ENTERED HOLDING PATTERN OVER FIELD, COMPLETED EMER CHKLIST, BROUGHT BACKUP SYS ON LINE AND NOTIFIED FLT ATTENDANT. NORMAL LNDG INITIATED. CAPT MADE LNDG. MADE USE OF COCKPIT RESOURCE TECHNICIANS AND EMER TRAINING. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR REVEALED THAT THE POST FLT INSPECTION SHOWED A FAILURE OF THE L SIDE HYD PUMP. THIS PUMP MALFUNCTIONED DURING THE LOWERING OF THE LNDG GEAR. SINCE IT IS AC PWRED BY THE 'AC WILD SYS' IT OVERLOADED THE AC WILD GENERATOR AND BLEW ITS CIRCUIT BREAKERS. THE CROSS TIE BUS RELAY THAT IS SUPPOSED TO CLOSE AT THIS POINT TO PWR THE HYD SYS FROM THE R (GREEN) SIDE FAILED TO OPERATE, NECESSITATING THE USE OF THE CHKLIST TO GET THE HYD AND ELECTRICAL PWR BACK INTO THE CORRECT SYS. THE 'WILD' AC GENERATOR IS ONLY PWRING THE HYD PUMPS WHEN THE PROPS ARE TURNING, PWRED THROUGH THE PROP REDUCTION GEAR BOX. THERE ARE 2 OTHER GENERATORS THAT RUN OFF THE ENGS BUT THEY DO NOT PWR THE AC WILD SYS PUMPS. THIS ACFT DOES NOT HAVE AN APU, IT HAS A PROP BRAKE ON THE R ENG AND THEREFORE CAN RUN THE R ENG AS AN APU WHILE 'BRAKING' THE PROP. RPTR FELT THAT THIS WAS AN ODD HAPPENING AND HAD NOT HAD ANY PRIOR EXPERIENCES LIKE THIS IN THE ATR-42.

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.