Corp aircraft has unsafe light when gear extended.

Attributes
ACN	205025
Time
Date	199203
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : agc
State Reference	PA
Altitude	agl bound lower : 0 agl bound upper : 0
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : pit tower : agc
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Recip Eng
Flight Phase	descent : approach landing other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : atp pilot : cfi pilot : instrument
Experience	flight time last 90 days : 50 flight time total : 4570 flight time type : 2000
ASRS Report	205025
Person 2
Affiliation	government : faa
Function	controller : local
Qualification	controller : non radar
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : unspecified other other : unspecified cockpit
Resolutory Action	flight crew : declared emergency flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

Problem arose when gear selector placed in down position to commence ILS 28 approach. Left main gear showed as unsafe. Passenger who has experience was sent back to visually inspect. Gear appeared to be down. Light bulb checked okay. Hydraulic pump checked okay. Reviewed emergency checklist. No further action indicated. Cycled gear with no results. Decided left main gear was down, but not locked. Advised ATC at onset of problem. Requested vectors off the ILS while reviewing situation. Upon evaluation, requested the ILS 28 approach and fire and rescue equipment. Attempted to lock gear with side load upon contacting runway with no improvement. Then slowed aircraft and made normal landing. Evacuated aircraft and secured on runway. No damage or injury. Upon visual inspection, I determined that over center lock was not engaged. Physically pushed lock in place. Reboarded aircraft and taxied to ramp. Gear lights came on upon startup and hydraulic returned to safety mode. Problem traced to binding of lock caused by weak spring and min clearance in housing. Clearance corrected by using smaller thickness spacing washers. New spring installed. ATC helpful by not constantly asking for information and updates. This allowed me to evaluate problem without interruption. Especially important in simple pilot operations. ATC was objective and professional, thus maintaining normal 'feeling' in cockpit, which helped keep anxiety levels down among passenger and crew.

Original NASA ASRS Text

Title: CORP ACFT HAS UNSAFE LIGHT WHEN GEAR EXTENDED.

Narrative: PROBLEM AROSE WHEN GEAR SELECTOR PLACED IN DOWN POS TO COMMENCE ILS 28 APCH. L MAIN GEAR SHOWED AS UNSAFE. PAX WHO HAS EXPERIENCE WAS SENT BACK TO VISUALLY INSPECT. GEAR APPEARED TO BE DOWN. LIGHT BULB CHKED OKAY. HYDRAULIC PUMP CHKED OKAY. REVIEWED EMER CHKLIST. NO FURTHER ACTION INDICATED. CYCLED GEAR WITH NO RESULTS. DECIDED L MAIN GEAR WAS DOWN, BUT NOT LOCKED. ADVISED ATC AT ONSET OF PROBLEM. REQUESTED VECTORS OFF THE ILS WHILE REVIEWING SITUATION. UPON EVALUATION, REQUESTED THE ILS 28 APCH AND FIRE AND RESCUE EQUIP. ATTEMPTED TO LOCK GEAR WITH SIDE LOAD UPON CONTACTING RWY WITH NO IMPROVEMENT. THEN SLOWED ACFT AND MADE NORMAL LNDG. EVACUATED ACFT AND SECURED ON RWY. NO DAMAGE OR INJURY. UPON VISUAL INSPECTION, I DETERMINED THAT OVER CTR LOCK WAS NOT ENGAGED. PHYSICALLY PUSHED LOCK IN PLACE. REBOARDED ACFT AND TAXIED TO RAMP. GEAR LIGHTS CAME ON UPON STARTUP AND HYD RETURNED TO SAFETY MODE. PROBLEM TRACED TO BINDING OF LOCK CAUSED BY WEAK SPRING AND MIN CLRNC IN HOUSING. CLRNC CORRECTED BY USING SMALLER THICKNESS SPACING WASHERS. NEW SPRING INSTALLED. ATC HELPFUL BY NOT CONSTANTLY ASKING FOR INFO AND UPDATES. THIS ALLOWED ME TO EVALUATE PROBLEM WITHOUT INTERRUPTION. ESPECIALLY IMPORTANT IN SIMPLE PLT OPS. ATC WAS OBJECTIVE AND PROFESSIONAL, THUS MAINTAINING NORMAL 'FEELING' IN COCKPIT, WHICH HELPED KEEP ANXIETY LEVELS DOWN AMONG PAX AND CREW.

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.