What happened
On January 14, 2013, a PIPER PA-34-220T, registration EC-IYV, was conducting a proficiency check flight at Jerez Airport. During the initial engine start sequence, the crew encountered difficulties starting the left engine, which resulted in the aircraft battery becoming discharged. Although the engines were eventually started using an external power source, the crew noted intermittent electrical issues during taxiing, specifically involving the loss of VOR and ADF indications and flickering communication displays when power was reduced.
Following takeoff, once the landing gear was retracted, the aircraft suffered a total electrical failure. All navigation and communication screens went dark, engine indicators dropped to zero, and the landing gear position indicators became inoperable. Fearing a total loss of power, the crew maintained a speed below 108 kt. The crew managed to restore instrument and radio communications by reducing the electrical load, specifically by disconnecting the pitot tube heating.
After verifying that the landing gear remained down and locked, the crew communicated with tower control and returned to Jerez, landing without further incident.
The investigation
The investigation focused on the cause of the electrical collapse. The aircraft's battery was removed and found to be completely exhausted, though it remained capable of holding a charge. To understand the failure mechanism, the operator performed ground simulations using an alternator, voltage regulator, and a battery setup.
Tests demonstrated that while a charged battery could handle loads exceeding alternator capacity, an exhausted battery could not. When external loads exceeded the alternator's production capacity, the system could not draw the necessary energy from the battery to compensate. This caused the voltage to drop below the threshold required to maintain the alternator's electromagnetic field, leading to the collapse of the alternator's magnetic field and a subsequent total loss of electrical production.
Findings
- The primary cause of the electrical failure was an exhausted battery combined with high electrical demand from the aircraft systems.
- The collapse of the alternator's magnetic field was triggered because the depleted battery could not provide the necessary energy to sustain the field when the load exceeded the alternator's output.
- The electrical overload indication can be misleading, as it may stem from a lack of production rather than an excess of demand, potentially causing pilots to misidentify the nature of the failure.
Safety action
Following the investigation, the operator, Flight Training Europe, updated its operating procedures. The new procedure prohibits the dispatch of any aircraft where the battery is unable to initiate engine rotation or start the engine without external assistance, unless the depleted battery is replaced with a functional one.