Narrative:

I was proceeding in mod turbulence in clear WX on an IFR flight plan en route from rapid city, sd to gunnison, co. Approximately 50 mi southwest of denver the aircraft autoplt began a steep climbing attitude. I observed we were losing altitude and airspeed. I promptly called ATC and informed them that I was experiencing difficulty, was unable to maintain my altitude and didn't know what the problem was. While we were communicating I observed the aircraft was nearly at a stall and still losing 300-400 FPM. She asked my intentions and I responded that I wanted to determine what the problem was before I decided. It descended to nearly 16,500 before I was able to stop the descent and then began to climb. ATC called and inquired if I would be able to maintain 17,000. I responded that I believed so and that I would attempt to return to the 18,000 assigned altitude. Shortly after this, I was handed off to the controller of the next sector. I was continuing to experience the severe downdrafts as well as updrafts and therefore was unable to hold FL180. The controller called me in the midst of this difficulty to inform me I had violated my assigned altitude and to phone ATC. I was hand flying the aircraft and attempting to avoid a disaster at that time. I replied, I was unable to copy the phone number. About 10 mins later things settled down and I called the controller and requested the phone #. I decided to file this report rather than call the chief controller to discuss my 'alleged' violation. The reporter was contacted to elicit information concerning aircraft confign at the time of mountain wave activity, and to determine if there has been an investigatory FAA followup. At the time of the mountain wave encounter, the aircraft had been flown by autoplt with the altitude hold engaged. Experiencing the downdraft, the pilot did not identify the wave activity as such, due to smooth flight conditions. Inexperience with mountain flying, and lack of familiarity with aircraft type led the pilot to believe that he might be experiencing some type of aircraft or engine problem. Discovery of adverse flight conditions was therefore delayed by some minutes, at which time the altitude hold was disengaged as per standard procedure. The reporter did not declare an emergency, nor did he contact the ARTCC supervisor as requested, fearing FAA punitive action.

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Original NASA ASRS Text

Title: PRIVATE SMA EXPERIENCES MOUNTAIN WAVE DOWNDRAFT IN VICINITY OF DEN AND IS UNABLE TO MAINTAIN ASSIGNED ALT.

Narrative: I WAS PROCEEDING IN MOD TURBULENCE IN CLEAR WX ON AN IFR FLT PLAN ENRTE FROM RAPID CITY, SD TO GUNNISON, CO. APPROX 50 MI SW OF DENVER THE ACFT AUTOPLT BEGAN A STEEP CLIMBING ATTITUDE. I OBSERVED WE WERE LOSING ALT AND AIRSPEED. I PROMPTLY CALLED ATC AND INFORMED THEM THAT I WAS EXPERIENCING DIFFICULTY, WAS UNABLE TO MAINTAIN MY ALT AND DIDN'T KNOW WHAT THE PROBLEM WAS. WHILE WE WERE COMMUNICATING I OBSERVED THE ACFT WAS NEARLY AT A STALL AND STILL LOSING 300-400 FPM. SHE ASKED MY INTENTIONS AND I RESPONDED THAT I WANTED TO DETERMINE WHAT THE PROBLEM WAS BEFORE I DECIDED. IT DESCENDED TO NEARLY 16,500 BEFORE I WAS ABLE TO STOP THE DSCNT AND THEN BEGAN TO CLIMB. ATC CALLED AND INQUIRED IF I WOULD BE ABLE TO MAINTAIN 17,000. I RESPONDED THAT I BELIEVED SO AND THAT I WOULD ATTEMPT TO RETURN TO THE 18,000 ASSIGNED ALT. SHORTLY AFTER THIS, I WAS HANDED OFF TO THE CTLR OF THE NEXT SECTOR. I WAS CONTINUING TO EXPERIENCE THE SEVERE DOWNDRAFTS AS WELL AS UPDRAFTS AND THEREFORE WAS UNABLE TO HOLD FL180. THE CTLR CALLED ME IN THE MIDST OF THIS DIFFICULTY TO INFORM ME I HAD VIOLATED MY ASSIGNED ALT AND TO PHONE ATC. I WAS HAND FLYING THE ACFT AND ATTEMPTING TO AVOID A DISASTER AT THAT TIME. I REPLIED, I WAS UNABLE TO COPY THE PHONE NUMBER. ABOUT 10 MINS LATER THINGS SETTLED DOWN AND I CALLED THE CTLR AND REQUESTED THE PHONE #. I DECIDED TO FILE THIS REPORT RATHER THAN CALL THE CHIEF CTLR TO DISCUSS MY 'ALLEGED' VIOLATION. THE REPORTER WAS CONTACTED TO ELICIT INFO CONCERNING ACFT CONFIGN AT THE TIME OF MOUNTAIN WAVE ACTIVITY, AND TO DETERMINE IF THERE HAS BEEN AN INVESTIGATORY FAA FOLLOWUP. AT THE TIME OF THE MOUNTAIN WAVE ENCOUNTER, THE ACFT HAD BEEN FLOWN BY AUTOPLT WITH THE ALT HOLD ENGAGED. EXPERIENCING THE DOWNDRAFT, THE PLT DID NOT IDENTIFY THE WAVE ACTIVITY AS SUCH, DUE TO SMOOTH FLT CONDITIONS. INEXPERIENCE WITH MOUNTAIN FLYING, AND LACK OF FAMILIARITY WITH ACFT TYPE LED THE PLT TO BELIEVE THAT HE MIGHT BE EXPERIENCING SOME TYPE OF ACFT OR ENGINE PROBLEM. DISCOVERY OF ADVERSE FLT CONDITIONS WAS THEREFORE DELAYED BY SOME MINUTES, AT WHICH TIME THE ALT HOLD WAS DISENGAGED AS PER STANDARD PROC. THE REPORTER DID NOT DECLARE AN EMER, NOR DID HE CONTACT THE ARTCC SUPVR AS REQUESTED, FEARING FAA PUNITIVE ACTION.

Data retrieved from NASA's ASRS site as of August 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.