Narrative:

Air ambulance flight, initially climbed to FL180. Large area of mountain wave ahead, so requested and was given climb to FL210 to try to top alto-cumulus standing lenticular clouds ahead and above. Through approximately FL200 aircraft cabin altitude warning light illuminated. Determined aircraft pressurization system was malfunctioning, and while troubleshooting, encountered mountain wave updraft which further distracted me from level off at FL210. As I pushed the nose over I noticed I was through FL215 and center called at FL216 to request my assigned altitude. I replied, 'FL210,' and center instructed me to 'maintain FL210, altitude indicates 21600'.' at that point I had power to idle and was leveling off in turbulence at FL210. Factors: faulty aircraft pressurization, mountain wave, inadequate monitoring of flight by PIC. Situation occurred because of PIC lack of monitoring flight INS while troubleshooting psi system. Mountain wave updraft contributed, but had I been flying first and troubleshooting second I may have caught updraft sooner and started corrective action to level off from increased climb rate. Suggestions: use autoplt with altitude select while troubleshooting systems. Anticipate level-off during troubleshooting system. The mountain wave should have been a key to think of updrafts and take care of them first before psi system.

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Original NASA ASRS Text

Title: AIR AMBULANCE ACFT ENCOUNTERS MOUNTAIN WAVE WHILE TROUBLESHOOTING PRESSURIZATION PROBLEM. ALT DEVIATION.

Narrative: AIR AMBULANCE FLT, INITIALLY CLBED TO FL180. LARGE AREA OF MOUNTAIN WAVE AHEAD, SO REQUESTED AND WAS GIVEN CLB TO FL210 TO TRY TO TOP ALTO-CUMULUS STANDING LENTICULAR CLOUDS AHEAD AND ABOVE. THROUGH APPROX FL200 ACFT CABIN ALT WARNING LIGHT ILLUMINATED. DETERMINED ACFT PRESSURIZATION SYS WAS MALFUNCTIONING, AND WHILE TROUBLESHOOTING, ENCOUNTERED MOUNTAIN WAVE UPDRAFT WHICH FURTHER DISTRACTED ME FROM LEVEL OFF AT FL210. AS I PUSHED THE NOSE OVER I NOTICED I WAS THROUGH FL215 AND CENTER CALLED AT FL216 TO REQUEST MY ASSIGNED ALT. I REPLIED, 'FL210,' AND CENTER INSTRUCTED ME TO 'MAINTAIN FL210, ALT INDICATES 21600'.' AT THAT POINT I HAD PWR TO IDLE AND WAS LEVELING OFF IN TURB AT FL210. FACTORS: FAULTY ACFT PRESSURIZATION, MOUNTAIN WAVE, INADEQUATE MONITORING OF FLT BY PIC. SITUATION OCCURRED BECAUSE OF PIC LACK OF MONITORING FLT INS WHILE TROUBLESHOOTING PSI SYS. MOUNTAIN WAVE UPDRAFT CONTRIBUTED, BUT HAD I BEEN FLYING FIRST AND TROUBLESHOOTING SECOND I MAY HAVE CAUGHT UPDRAFT SOONER AND STARTED CORRECTIVE ACTION TO LEVEL OFF FROM INCREASED CLB RATE. SUGGESTIONS: USE AUTOPLT WITH ALT SELECT WHILE TROUBLESHOOTING SYSTEMS. ANTICIPATE LEVEL-OFF DURING TROUBLESHOOTING SYS. THE MOUNTAIN WAVE SHOULD HAVE BEEN A KEY TO THINK OF UPDRAFTS AND TAKE CARE OF THEM FIRST BEFORE PSI SYS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.