Electrical System Malfunction During Night IMC
You are on a night IFR flight in a single-engine turboprop at 12,000 ft in IMC. The aircraft has a 28 V DC electrical system with a 200 A alternator and a 24 V lead-acid battery. The alternator caution light illuminates, and the ammeter shows a 20 A discharge. The battery voltage is 24.5 V and decreasing slowly. You have two Garmin G1000 displays, one primary flight display (PFD) and one multifunction display (MFD), both essential for navigation. The autopilot is engaged. You are 40 minutes from your destination, with an alternate 20 minutes further. The weather at destination is 800 ft ceiling and 2 miles visibility, with a 15 kt crosswind. There is no icing. You have a standby attitude indicator and a standby altimeter and airspeed indicator, all powered by the battery. The landing gear and flaps are electrically actuated.
1. What is the immediate priority and what steps would you take to manage the electrical load?
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The immediate priority is to preserve battery power for essential systems and to prepare for a possible total electrical failure. The 20 A discharge indicates the alternator is offline or failing. At 24.5 V and decreasing, the battery has limited capacity. You should first reduce electrical load by turning off non-essential equipment: cabin lights, unnecessary avionics (e.g., second COM, weather radar if not needed), pitot heat if not in icing (but it is night IMC, so pitot heat may be necessary; however, it draws significant current, so balance), and any entertainment systems.
Next, attempt to reset the alternator: cycle the alternator switch off then on, check the alternator circuit breaker (do not reset if it has popped and smells hot). If the alternator does not come back online, plan for a total loss of electrical power. You should notify ATC of your situation and request priority handling. Consider diverting to the closer alternate if it has better weather or if you are unsure of battery endurance.
You should also consider shedding the autopilot if it is electric and not required; hand-fly to reduce load. However, the autopilot may reduce workload in IMC. The key is to calculate battery endurance: a 24 V battery with, say, 20 Ah capacity at 20 A discharge would last about 1 hour, but voltage is already dropping, so less. You have 40 minutes to destination; if you shed load to essential only (PFD, one COM, one NAV, transponder, standby instruments), the battery may last. But you must be prepared for the displays to fail.
You should brief the approach: if electrical power fails, you will use the standby instruments and fly a partial-panel approach. The landing gear and flaps are electrically actuated; without power, you may not be able to extend them. You need to check the emergency gear extension procedure (often a manual release) and plan for a no-flap landing. This may require a longer runway and higher approach speed.
2. If the battery voltage continues to drop and the PFD and MFD begin to flicker, what would you do?
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If the displays flicker, you are close to losing primary flight information. You should immediately transition to the standby instruments: attitude indicator, altimeter, and airspeed indicator. These are battery-powered and should remain available. You should also prepare for the loss of the autopilot, which may disconnect when power drops. Hand-fly the aircraft using the standby instruments and the magnetic compass.
At this point, you should declare an emergency with ATC, stating that you have lost primary electrical power and are on standby instruments. Request vectors to the nearest suitable airport, preferably one with better weather and a long runway. If the destination weather is 800 ft and 2 miles, that is close to minimums; consider the alternate if it has better conditions.
You must also consider the landing gear and flaps. If they are electrically actuated, you will need to use the emergency extension system. This may involve a manual crank or a nitrogen bottle. You should review the procedure now, before power is lost completely. If the gear cannot be extended, you will need to land gear-up, which is a serious emergency.
In the final approach, use the standby instruments to fly a precision or non-precision approach. If the standby attitude indicator is reliable, you can fly an ILS if available. Otherwise, use a localizer or GPS approach with the standby instruments.
After landing, you should expect to lose all electrical power, including radios and lights. You should have a flashlight ready. The key judgement is to recognise the point at which you must abandon the primary displays and rely on standby instruments, and to manage the aircraft's configuration early to avoid a rushed approach.