Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 100; Flight Crew Total 700; Flight Crew Type 200
Confusion
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Other / Unknown
Flight Crew Diverted; Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft
While on final approach for ILS we had a complete electrical failure. We lost HSI; Loc; glideslope; Navs; coms; transponder; rpm gauge; everything. It was VMC when the failure happened and we were about to descend into an overcast layer around 800 FT MSL without any ground reference. Per ATC Approach instruction; upon going missed we climbed to 2000 FT MSL and flew runway heading with our magnetic compass. We maintained 2000 FT to maintain VFR due to layers above and beneath us. After running through all of the relative checklist with no changes; I decided to fly to an uncontrolled airport to land after exiting the airspace. While performing an emergency gear extension; we regained total electrical power. I determined that the failure was related to the gear switch. After putting the gear down on the approach is when our HSI and NAVs failed. When we went missed and picked the gear up; we lost all electrical power before I could advise Tower of the situation. I attempted to transmit our condition and situation just in case they could hear us. We could not squawk 7600 due to the failure. After lowering the gear for the emergency gear extension and immediately recovering electrical power is when I realized it must be related to an electrical issue with the gear switch. After regaining power I contacted ATC approach on 121.1 and let them know what happened. After we landed; I called Tower and informed them of the problem as well.
Reporter stated the PA-44 was equipped with a Standard six-pack; round gauges and two Garmins. The Landing Gear 'Extend/Retract' handle is electric and to the left of the Throttles. The Emergency Extend 'Pull' switch; a round Red knob; just to the left of the normal gear handle.Reporter stated he never actually got to the item on the Emergency CheckList that says to pull the Emergency Extend switch because the first item on the list says to 'Extend' the landing gear. When he did that; the gear extended and locked down (three Green lights) and the hydraulic pump stopped; that's when all electrical came back. Maintenance later told him the aircraft battery was weak and would not hold much of an electrical load. As a result; when he had selected 'Up' (retract); the electric hydraulic pump continued to run even with the gear up; until 1400 psi hydraulic pressure has been reached. The PA-44 Landing gears do not have uplocks; continuous hydraulic pressure is used to keep the gears up and locked. With the aircraft battery being weak; even with two Alternators functioning; not enough electrical power was available and the electrical system shut-down until the hydraulic pump no longer was required to keep running to maintain 1400 psi pressure. No Circuit Breakers (C/B) had popped. The hydraulic pump is aft of the baggage bulkhead. The Emergency Extend pull switch routes hydraulic fluid from the hydraulic pressure 'Up' side so the gears can free fall.
A Flight Instructor reports losing his HSI and navigation on approach when he extended the landing gear on their Piper PA-44 Seminole aircraft. Due to the missed approach; he retracted the gear and then lost all electrical power and indications; except for the magnetic compass and vacuum gauges.