Narrative:

Departed bfl in small aircraft on IFR flight plan from bfl to bur, cleared to bur via radar vectors lake hughes VOR (lhs), lhs.LYNXX6 arrival, maintain 9000. Tracking 140 degrees inbound to lhs, route of flight crosses tehachapi mountains, western corner of antelope valley, and lhs VOR in the san gabriel mountains. Southerly winds approximately 20 KTS and greater set up mountain wave activity in vicinity of these mountain ranges, and the ranges were mostly obscured in clouds, most tops estimated at 8000, but with several buildups over 9000, and occasional buildups beyond 11000 within 10 NM of route. A significant storm with tops greater than 30000 was within 50 mi to the west, but was not a factor in this flight. Visibility outside of clouds was unrestricted. Approximately 20 NM northwest of lhs, approaching tehachapi mountains, encountered downdraft from mountain wave. Slowed to best rate of climb and was still losing 300-500 FPM. Advised la center controller that I was unable to maintain altitude (was probably down to 8500-8600 by this time), controller asked flight conditions, which were still VMC but would enter IMC within a half mi. Controller advised that we were descending below a min vectoring altitude, and recommended 180 degree turn and return to bfl. I requested and was approved for a deviation to the west, intending to attempt a look around the buildup that was in my intended flight path. Still losing altitude, it quickly became clear that this deviation was not workable, so I continued a turn to approximately 310. Asked intentions, I requested a climb to 11000 to make another attempt at higher altitude, which was approved. The controller checked with another aircraft small aircraft X which had just made the same crossing at 11000, and had lost considerable airspeed in order to maintain altitude, but had been able to get through. We had to fly several mi north to get out of the downdraft, probably dropping below 8000 at one point, but eventually were able to climb, and once we reached 10000, the controller turned us back to lhs, and we were able to continue a climb to 11000. In fact, updrafts carried us to as high as 11400. As we entered the downdraft again, the controller cleared us for a gradual descent back to 9000. Starting our crossing at 11000 with plenty of cloud clearance, and maintaining best rate of climb, we still lost between 100-500 FPM, descending, I believe, to just under 9000 in VMC before crossing into the windward updrafts, which carried us to altitudes varying between 9500 and 10000 as we crossed the antelope valley. Within 5 NM of lhs we encountered the leeward downdrafts of the next mountain range. Starting at about 9500, we lost 100-200 FPM, finally breaking out of the downdrafts at about 8600, still maintaining VMC. At some point in this period, asked by controller of conditions, I responded that I was still losing 100 FPM, but that I had adequate cloud clearance to complete the crossing in VMC and would continue. Beyond lhs, with burbank approach, the remainder of the flight was uneventful, although at times it was still difficult to maintain assigned altitude, more due to updrafts. While the flight was completed successfully, I have spent some time second guessing my actions. Based on my WX briefings (which were reasonably accurate), should I have even attempted this flight? Once encountering difficulty, should I have retreated to bakersfield? Based on conditions, could I have planned my crossing differently? Did I communicate my predicament and intentions accurately and in a timely manner to ATC?

Google
 

Original NASA ASRS Text

Title: SMA ENCOUNTERS MOUNTAIN WAVE DOWNDRAFTS, UNABLE HOLD ASSIGNED ALT. CTLR SUGGESTS 180 TURN AS DSNDING BELOW RADAR VECTORING ALT. RPTR TURNS, CLBS, CONTINUES ON ORIGINAL COURSE.

Narrative: DEPARTED BFL IN SMA ON IFR FLT PLAN FROM BFL TO BUR, CLRED TO BUR VIA RADAR VECTORS LAKE HUGHES VOR (LHS), LHS.LYNXX6 ARR, MAINTAIN 9000. TRACKING 140 DEGS INBOUND TO LHS, RTE OF FLT CROSSES TEHACHAPI MOUNTAINS, WESTERN CORNER OF ANTELOPE VALLEY, AND LHS VOR IN THE SAN GABRIEL MOUNTAINS. SOUTHERLY WINDS APPROX 20 KTS AND GREATER SET UP MOUNTAIN WAVE ACTIVITY IN VICINITY OF THESE MOUNTAIN RANGES, AND THE RANGES WERE MOSTLY OBSCURED IN CLOUDS, MOST TOPS ESTIMATED AT 8000, BUT WITH SEVERAL BUILDUPS OVER 9000, AND OCCASIONAL BUILDUPS BEYOND 11000 WITHIN 10 NM OF RTE. A SIGNIFICANT STORM WITH TOPS GREATER THAN 30000 WAS WITHIN 50 MI TO THE W, BUT WAS NOT A FACTOR IN THIS FLT. VISIBILITY OUTSIDE OF CLOUDS WAS UNRESTRICTED. APPROX 20 NM NW OF LHS, APCHING TEHACHAPI MOUNTAINS, ENCOUNTERED DOWNDRAFT FROM MOUNTAIN WAVE. SLOWED TO BEST RATE OF CLB AND WAS STILL LOSING 300-500 FPM. ADVISED LA CTR CTLR THAT I WAS UNABLE TO MAINTAIN ALT (WAS PROBABLY DOWN TO 8500-8600 BY THIS TIME), CTLR ASKED FLT CONDITIONS, WHICH WERE STILL VMC BUT WOULD ENTER IMC WITHIN A HALF MI. CTLR ADVISED THAT WE WERE DSNDING BELOW A MIN VECTORING ALT, AND RECOMMENDED 180 DEG TURN AND RETURN TO BFL. I REQUESTED AND WAS APPROVED FOR A DEV TO THE W, INTENDING TO ATTEMPT A LOOK AROUND THE BUILDUP THAT WAS IN MY INTENDED FLT PATH. STILL LOSING ALT, IT QUICKLY BECAME CLR THAT THIS DEV WAS NOT WORKABLE, SO I CONTINUED A TURN TO APPROX 310. ASKED INTENTIONS, I REQUESTED A CLB TO 11000 TO MAKE ANOTHER ATTEMPT AT HIGHER ALT, WHICH WAS APPROVED. THE CTLR CHKED WITH ANOTHER ACFT SMA X WHICH HAD JUST MADE THE SAME XING AT 11000, AND HAD LOST CONSIDERABLE AIRSPD IN ORDER TO MAINTAIN ALT, BUT HAD BEEN ABLE TO GET THROUGH. WE HAD TO FLY SEVERAL MI N TO GET OUT OF THE DOWNDRAFT, PROBABLY DROPPING BELOW 8000 AT ONE POINT, BUT EVENTUALLY WERE ABLE TO CLB, AND ONCE WE REACHED 10000, THE CTLR TURNED US BACK TO LHS, AND WE WERE ABLE TO CONTINUE A CLB TO 11000. IN FACT, UPDRAFTS CARRIED US TO AS HIGH AS 11400. AS WE ENTERED THE DOWNDRAFT AGAIN, THE CTLR CLRED US FOR A GRADUAL DSCNT BACK TO 9000. STARTING OUR XING AT 11000 WITH PLENTY OF CLOUD CLRNC, AND MAINTAINING BEST RATE OF CLB, WE STILL LOST BTWN 100-500 FPM, DSNDING, I BELIEVE, TO JUST UNDER 9000 IN VMC BEFORE XING INTO THE WINDWARD UPDRAFTS, WHICH CARRIED US TO ALTS VARYING BTWN 9500 AND 10000 AS WE CROSSED THE ANTELOPE VALLEY. WITHIN 5 NM OF LHS WE ENCOUNTERED THE LEEWARD DOWNDRAFTS OF THE NEXT MOUNTAIN RANGE. STARTING AT ABOUT 9500, WE LOST 100-200 FPM, FINALLY BREAKING OUT OF THE DOWNDRAFTS AT ABOUT 8600, STILL MAINTAINING VMC. AT SOME POINT IN THIS PERIOD, ASKED BY CTLR OF CONDITIONS, I RESPONDED THAT I WAS STILL LOSING 100 FPM, BUT THAT I HAD ADEQUATE CLOUD CLRNC TO COMPLETE THE XING IN VMC AND WOULD CONTINUE. BEYOND LHS, WITH BURBANK APCH, THE REMAINDER OF THE FLT WAS UNEVENTFUL, ALTHOUGH AT TIMES IT WAS STILL DIFFICULT TO MAINTAIN ASSIGNED ALT, MORE DUE TO UPDRAFTS. WHILE THE FLT WAS COMPLETED SUCCESSFULLY, I HAVE SPENT SOME TIME SECOND GUESSING MY ACTIONS. BASED ON MY WX BRIEFINGS (WHICH WERE REASONABLY ACCURATE), SHOULD I HAVE EVEN ATTEMPTED THIS FLT? ONCE ENCOUNTERING DIFFICULTY, SHOULD I HAVE RETREATED TO BAKERSFIELD? BASED ON CONDITIONS, COULD I HAVE PLANNED MY XING DIFFERENTLY? DID I COMMUNICATE MY PREDICAMENT AND INTENTIONS ACCURATELY AND IN A TIMELY MANNER TO ATC?

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.