If an aircraft cruising in RVSM airspace (FL290–FL410) within Bahrain FIR reports that its automatic altitude-keeping device or primary altimeter has failed, what immediate action must the controller take?

1. Establish a minimum of 2,000 ft vertical separation (or appropriate horizontal radar separation) from all other aircraft and coordinate non-RVSM status with adjacent sectors
2. Immediately clear the aircraft to descend to 1,000 ft AMSL without coordinating with other traffic
3. Instruct the aircraft to switch off its transponder to prevent false collision warnings
4. Advise the pilot that no action is necessary as long as the backup mechanical airspeed indicator works