BE18 pilot reports landing gear collapse during takeoff roll.

Attributes
ACN	785764
Time
Date	200805
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 0
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	general aviation : personal
Make Model Name	Twin Beech 18
Operating Under FAR Part	Part 91
Flight Phase	ground : takeoff roll
Flight Plan	None
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : commercial pilot : multi engine pilot : private
Experience	flight time last 90 days : 130 flight time total : 1800 flight time type : 30
ASRS Report	785764
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : unable
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Normal preflight; engine start; and taxi. Normal run-up. Takeoff power and at approximately 60 KTS; right main gear and left main gear collapsed. Aircraft slid to a stop on runway centerline. Notified tower of problem; shut down all switches; and turned fuel off. Landing gear switch remained in down position with green light and no warning horn throughout entire event. Callback conversation with reporter revealed the following information: under normal circumstances the circuit which runs the landing gear motor passes through the squat switch and the landing gear switch; which prevents the gear from being raised inadvertently with the aircraft on the ground. The departure runway has undulations which cause the aircraft to come off the squat switch as flying speed is reached. It was at this point that the gear retracted even though the gear switch was still in the down position. A crane was brought in to raise the aircraft so the landing gear could be extended and pinned for the tow back to the hangar. When the master switch was turned on the landing gear extended even though the landing gear switch had never been touched and remained in the down position. No electrical faults have been discovered and no reason for the incident has been found.

Original NASA ASRS Text

Title: BE18 PILOT REPORTS LANDING GEAR COLLAPSE DURING TKOF ROLL.

Narrative: NORMAL PREFLT; ENG START; AND TAXI. NORMAL RUN-UP. TKOF PWR AND AT APPROX 60 KTS; R MAIN GEAR AND L MAIN GEAR COLLAPSED. ACFT SLID TO A STOP ON RWY CTRLINE. NOTIFIED TWR OF PROB; SHUT DOWN ALL SWITCHES; AND TURNED FUEL OFF. LNDG GEAR SWITCH REMAINED IN DOWN POS WITH GREEN LIGHT AND NO WARNING HORN THROUGHOUT ENTIRE EVENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: UNDER NORMAL CIRCUMSTANCES THE CIRCUIT WHICH RUNS THE LANDING GEAR MOTOR PASSES THROUGH THE SQUAT SWITCH AND THE LANDING GEAR SWITCH; WHICH PREVENTS THE GEAR FROM BEING RAISED INADVERTENTLY WITH THE ACFT ON THE GROUND. THE DEPARTURE RWY HAS UNDULATIONS WHICH CAUSE THE ACFT TO COME OFF THE SQUAT SWITCH AS FLYING SPEED IS REACHED. IT WAS AT THIS POINT THAT THE GEAR RETRACTED EVEN THOUGH THE GEAR SWITCH WAS STILL IN THE DOWN POSITION. A CRANE WAS BROUGHT IN TO RAISE THE ACFT SO THE LANDING GEAR COULD BE EXTENDED AND PINNED FOR THE TOW BACK TO THE HANGAR. WHEN THE MASTER SWITCH WAS TURNED ON THE LANDING GEAR EXTENDED EVEN THOUGH THE LANDING GEAR SWITCH HAD NEVER BEEN TOUCHED AND REMAINED IN THE DOWN POSITION. NO ELECTRICAL FAULTS HAVE BEEN DISCOVERED AND NO REASON FOR THE INCIDENT HAS BEEN FOUND.

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.