Night VFR into Bahrain with a Failing Alternator

The immediate priority is to preserve battery power for the equipment needed to safely complete the approach, landing, and any required communications. The steady discharge plus the low-voltage light indicates the alternator has failed or is failing, so every consumer is now draining a finite battery.

Actions in order:

1. Shed non-essential load at once: pitot heat only if icing is possible (not here), landing/taxi lights off until short final, cabin floodlight off, unnecessary avionics off, and any entertainment or convenience equipment off. Keep one COM, one NAV, the transponder, and the essential flight instruments.
2. Notify ATC early rather than late. Declare the electrical failure on the current frequency while the main radio still works, state your position, altitude, intentions, and that you may lose two-way radio. Request a shortened routing and priority handling into Bahrain.
3. Prepare the handheld radio now, not later: set it to the expected frequencies, test it, and keep it accessible.
4. Continue toward Bahrain only if the battery state allows the required radio and navigation for the Class C clearance; otherwise divert to the lit alternate while you still have power and daylight-independent navigation.
5. Plan for a possible total electrical failure: brief yourself on lost transponder, lost landing light, and the need for light signals. A steady green from the tower means cleared to land; a flashing red means give way and continue circling.

The judgement point is that continuing into busy Class C airspace with a dying battery and no transponder increases risk to everyone; the diversion decision must be made while you still have the power to coordinate it.

Class C airspace requires a clearance and normally a serviceable transponder. If the transponder fails, you must tell ATC immediately; they may still clear you in with a discrete code of 7600 if the radio fails, or they may restrict you. If the main radio fails, you squawk 7600 if the transponder still works, and you proceed according to the last clearance and expected light signals.

Practical sequence:

• Before failure: tell Approach your electrical state and ask for the shortest safe routing and an early descent.
• On radio failure: set 7600, continue on your last acknowledged clearance, and watch the tower for light signals.
• If both radio and transponder fail: you are effectively a NORDO aircraft in controlled airspace. The safest course is to divert to the uncontrolled or less congested alternate unless Bahrain Approach has already cleared you to enter and land.

The key judgement is that entering Class C without a clearance or without a working transponder is a serious airspace infringement; the alternate exists precisely so you do not have to force the issue.

A 15 A discharge on a typical light-aircraft battery of, say, 25 Ah means roughly 1.5 hours from full charge to complete depletion, less in practice because battery capacity falls with age and cold and because voltage sags before the charge is exhausted. Essential avionics might draw 5–8 A, so after shedding load you may extend useful time to perhaps 2 hours, but you should plan on losing power sooner than the arithmetic suggests.

Decision use:

• Estimate time to destination: 45 NM at, say, 120 kt groundspeed is about 22 minutes. That is comfortably within battery endurance if you shed load now.
• Keep a reserve for the approach, landing, and taxi, and for the handheld radio.
• If the destination requires holding or a long vector, the margin shrinks; the alternate at 30 NM is a safer bet if you are given delaying instructions.

The examiner is testing whether you convert a discharge rate into a time budget and act before the budget runs out, rather than waiting for the battery to die over the airport.