After an unsafe gear indication on final approach, reporter pilot did a go around, trouble-shot, got...

Attributes
ACN	333378
Time
Date	199604
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : bdl
State Reference	CT
Altitude	agl bound lower : 1500 agl bound upper : 1500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : bdl
Operator	general aviation : personal
Make Model Name	Piper Single Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Flight Phase	descent : approach landing other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private pilot : instrument
Experience	flight time last 90 days : 120 flight time total : 2629 flight time type : 900
ASRS Report	333378
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 flight crewa
Resolutory Action	flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

The problem occurred while I was on an ILS approach in VMC conditions into bdl, ct, on apr/xx/96. As I crossed the OM and actuated the landing gear switch, I noted that the normal 3 green lights did not appear. At the time there was enough turbulence to cause me to be uncertain as to whether the gear had descended or not. And as it is not possible to observe the gear condition from the cockpit of the piper malibu, I informed the tower of my problem and requested that I break off the approach, leave the area and circle outside the control zone to try to ascertain the problem. This was approved and I was handed back to approach control. While circling in the designated area, I pulled and reset the circuit breakers and followed other emergency procedures in the poh, including recycling the landing gear, at which point the gear indicator lights returned and indicated a normal gear down position. I then requested a flyby of the tower to confirm this, which was approved, and both tower and ground personnel reported that the gear appeared to be down and locked. I was then cleared to land and the landing was uneventful, although I was followed by the crash equipment after touchdown and during the rollout. I subsequently had the plane jacked up and the gear swung at an authority/authorized piper malibu maintenance facility, and they determined that a microswitch in the gear circuitry had a higher than normal contact resistance, resulting in an intermittent failure mode. The switch assembly was replaced with a properly functioning unit, and the gear recycled a number of times with no further problems. The problem has not reoccurred in a further 40 hours of flight time. A failure of this type is not readily prevented by routine maintenance, as the switch in question has a very low failure rate and is not normally inspected. In this case it had not actually failed but was intermittent. It is even more difficult when the failure is intermittent, and only a good diagnostic technician was able to find the fault after several hours of trouble-shooting.

Original NASA ASRS Text

Title: AFTER AN UNSAFE GEAR INDICATION ON FINAL APCH, RPTR PLT DID A GAR, TROUBLE-SHOT, GOT A GOOD GEAR DOWN INDICATION, HAD IT CHKED BY TWR ON A FLY-BY AND LANDED UNEVENTFULLY. CAUSED BY BAD MICRO SWITCH THAT HAD A HIGHER THAN NORMAL CONTACT RESISTANCE.

Narrative: THE PROB OCCURRED WHILE I WAS ON AN ILS APCH IN VMC CONDITIONS INTO BDL, CT, ON APR/XX/96. AS I CROSSED THE OM AND ACTUATED THE LNDG GEAR SWITCH, I NOTED THAT THE NORMAL 3 GREEN LIGHTS DID NOT APPEAR. AT THE TIME THERE WAS ENOUGH TURB TO CAUSE ME TO BE UNCERTAIN AS TO WHETHER THE GEAR HAD DSNDED OR NOT. AND AS IT IS NOT POSSIBLE TO OBSERVE THE GEAR CONDITION FROM THE COCKPIT OF THE PIPER MALIBU, I INFORMED THE TWR OF MY PROB AND REQUESTED THAT I BREAK OFF THE APCH, LEAVE THE AREA AND CIRCLE OUTSIDE THE CTL ZONE TO TRY TO ASCERTAIN THE PROB. THIS WAS APPROVED AND I WAS HANDED BACK TO APCH CTL. WHILE CIRCLING IN THE DESIGNATED AREA, I PULLED AND RESET THE CIRCUIT BREAKERS AND FOLLOWED OTHER EMER PROCS IN THE POH, INCLUDING RECYCLING THE LNDG GEAR, AT WHICH POINT THE GEAR INDICATOR LIGHTS RETURNED AND INDICATED A NORMAL GEAR DOWN POS. I THEN REQUESTED A FLYBY OF THE TWR TO CONFIRM THIS, WHICH WAS APPROVED, AND BOTH TWR AND GND PERSONNEL RPTED THAT THE GEAR APPEARED TO BE DOWN AND LOCKED. I WAS THEN CLRED TO LAND AND THE LNDG WAS UNEVENTFUL, ALTHOUGH I WAS FOLLOWED BY THE CRASH EQUIP AFTER TOUCHDOWN AND DURING THE ROLLOUT. I SUBSEQUENTLY HAD THE PLANE JACKED UP AND THE GEAR SWUNG AT AN AUTH PIPER MALIBU MAINT FACILITY, AND THEY DETERMINED THAT A MICROSWITCH IN THE GEAR CIRCUITRY HAD A HIGHER THAN NORMAL CONTACT RESISTANCE, RESULTING IN AN INTERMITTENT FAILURE MODE. THE SWITCH ASSEMBLY WAS REPLACED WITH A PROPERLY FUNCTIONING UNIT, AND THE GEAR RECYCLED A NUMBER OF TIMES WITH NO FURTHER PROBS. THE PROB HAS NOT REOCCURRED IN A FURTHER 40 HRS OF FLT TIME. A FAILURE OF THIS TYPE IS NOT READILY PREVENTED BY ROUTINE MAINT, AS THE SWITCH IN QUESTION HAS A VERY LOW FAILURE RATE AND IS NOT NORMALLY INSPECTED. IN THIS CASE IT HAD NOT ACTUALLY FAILED BUT WAS INTERMITTENT. IT IS EVEN MORE DIFFICULT WHEN THE FAILURE IS INTERMITTENT, AND ONLY A GOOD DIAGNOSTIC TECHNICIAN WAS ABLE TO FIND THE FAULT AFTER SEVERAL HRS OF TROUBLE-SHOOTING.

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.

After an unsafe gear indication on final approach, reporter pilot did a go around, trouble-shot, got a good gear down indication, had it checked by tower on a fly-by and landed uneventfully. Caused by bad micro switch that had a higher than normal contact resistance.