Flight Crew Commercial
Situational Awareness
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; General Declared Emergency; General Maintenance Action
Aircraft
During return trip to home base; after dropping off patient; transmission chip light came on. Power was immediately reduced and a landing area was selected. The only suitable landing area was a military airfield. I informed Approach I had a mechanical problem and requested to divert into the military airfield. I was told to change over to the Tower. I informed them I had a mechanical problem; and was told I could not land without a Prior Permission Request (PPR); or declaring an emergency. I choose to declare an emergency. During the descent into the airfield I monitored the transmission temperatures and pressures; both seemed to hold steady during the descent. After landing aircraft was shutdown and Mechanic was notified. No further incident occurred. After further inspection of the aircraft the Mechanic noticed that the compressor shaft on the air conditioning unit had sheared off. The oil sample taken showed that the metal on the chip detector was consistent with the metal on the sheared shaft; and not the transmission gears.
An EC135 transmission chip light illuminated so the pilot declared an emergency and diverted to a nearby military airfield where it was later determined that a failed air conditioning shaft caused metal in the oil.