Beech King Air 250 pilot reported a cabin decompression during cruise at 27;000 feet resulting in an immediate descent and landing.
Synopsis
Beech King Air 250 pilot reported a cabin decompression during cruise at 27;000 feet resulting in an immediate descent and landing.
Narrative
I was level at 27;000 feet on a flight to ZZZ. Had just finished deviating around some weather and then descended to 27;000 from FL290 to stay under a cloud layer. The air was smooth. My cabin started to depressurize slowly and then it quickly depressurized over about 30 second (i.e. not explosive decompression). I put on the mask; started the descent; keyed the mike; called ATC and then got distracted trying to disconnect the autothrottles. I looked at the TCAS; there was no one near so just pushed the plane over and got the descent started. I finally realized I had keyed the mike but not declared my intentions so [requested priority handling] and asked for 10;000 feet. Was immediately given the requested altitude.Don't know what caused this yet; the aircraft had been fine when it was dropped off for the maintenance inspection; then the plane had been used to test equipment for an STC (Supplemental Type Certificate). Do not know if any of that work involved the pressurization system. I do know that it tested properly on the ground and pressurized right after takeoff.
NASA callback
Reporter stated that during post flight maintenance inspection it was found that the two pressurization lines to the controller had somehow been reversed during an installation; however there was no record of such a procedure having been done. When the controller malfunctioned during the flight; it reversed airflow.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.