Narrative:

I was giving flight instructions in a two-place glider in wave flying; a meteorological condition that enables very high altitude soaring flight as a result of high speed wind crossing the mountains and setting up a series of standing waves downwind of the mountain crest. This type of flight is frequently made above FL180 by entering a 'wave window' set up under a letter of agreement with center and opened on an 'as-needed' basis. We made the request to center to open the window when we were at approximately 15000 ft and climbing; and center asked us to hold for 30 mins below FL180 while they cleared traffic out of the wave window. Holding in wave involves matching airspeed with wind speed to maintain position and using lift-canceling devices (spoilers) to prevent further climb. During our 30 min hold I believe the wind speed increased; pushing us further downwind (backwards). I think the stationary clouds in front of and behind us also grew in size; although I did not take note of that circumstance at the time. After the 30 min hold we resumed our climb and were enveloped very quickly at about 23500 ft by the cloud behind us. I took control from the student and immediately picked up the speed to see if we could fly forward out of the cloud but waited only a few seconds before deciding that we were at risk of becoming disoriented and entering a dangerous flight regime without outside reference or instruments for IFR flight. Part of what prompted my concern was having read NTSB reports of people becoming disoriented inside of a min and entering a death spiral. I did not want to risk such an eventuality; so resorted to the 'benign spiral mode;' a maneuver the manufacturer of this model of glider recommends as a means to make a stabilized descent without touching the controls. This maneuver calls for the pilot to pull the trim full aft and to pull on full spoilers; then allow the glider to descend without touching the controls. The glider descended in a benign spiral for a little over 5 mins; breaking out below the clouds at about 11000 ft MSL (approximately 6500 ft AGL). I knew in advance that cloud base was sufficiently high that we would break out well above the ground. In retrospect I should have paid more attention to the position of the airplane relative to the stationary cloud behind me; as I believe the wind speed increased during our hold below FL180. I should also have encouraged the student pilot to fly further out into the gap between the stationary clouds; an upwind move that would have kept us further from the cloud behind us. I have incorporated these techniques into subsequent flight practice.

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Original NASA ASRS Text

Title: INSTRUCTOR AND STUDENT PLT ABOARD GROB SAILPLANE ARE SOARING AT FL220 WHEN STRONG RISING WINDS LIFT THEM INTO IMC CONDITIONS. EXIT USING BENIGN SPIRAL TECHNIQUE.

Narrative: I WAS GIVING FLT INSTRUCTIONS IN A TWO-PLACE GLIDER IN WAVE FLYING; A METEOROLOGICAL CONDITION THAT ENABLES VERY HIGH ALT SOARING FLT AS A RESULT OF HIGH SPEED WIND CROSSING THE MOUNTAINS AND SETTING UP A SERIES OF STANDING WAVES DOWNWIND OF THE MOUNTAIN CREST. THIS TYPE OF FLT IS FREQUENTLY MADE ABOVE FL180 BY ENTERING A 'WAVE WINDOW' SET UP UNDER A LETTER OF AGREEMENT WITH CTR AND OPENED ON AN 'AS-NEEDED' BASIS. WE MADE THE REQUEST TO CTR TO OPEN THE WINDOW WHEN WE WERE AT APPROX 15000 FT AND CLBING; AND CTR ASKED US TO HOLD FOR 30 MINS BELOW FL180 WHILE THEY CLRED TFC OUT OF THE WAVE WINDOW. HOLDING IN WAVE INVOLVES MATCHING AIRSPEED WITH WIND SPEED TO MAINTAIN POS AND USING LIFT-CANCELING DEVICES (SPOILERS) TO PREVENT FURTHER CLB. DURING OUR 30 MIN HOLD I BELIEVE THE WIND SPD INCREASED; PUSHING US FURTHER DOWNWIND (BACKWARDS). I THINK THE STATIONARY CLOUDS IN FRONT OF AND BEHIND US ALSO GREW IN SIZE; ALTHOUGH I DID NOT TAKE NOTE OF THAT CIRCUMSTANCE AT THE TIME. AFTER THE 30 MIN HOLD WE RESUMED OUR CLB AND WERE ENVELOPED VERY QUICKLY AT ABOUT 23500 FT BY THE CLOUD BEHIND US. I TOOK CTL FROM THE STUDENT AND IMMEDIATELY PICKED UP THE SPEED TO SEE IF WE COULD FLY FORWARD OUT OF THE CLOUD BUT WAITED ONLY A FEW SECONDS BEFORE DECIDING THAT WE WERE AT RISK OF BECOMING DISORIENTED AND ENTERING A DANGEROUS FLT REGIME WITHOUT OUTSIDE REFERENCE OR INSTRUMENTS FOR IFR FLT. PART OF WHAT PROMPTED MY CONCERN WAS HAVING READ NTSB RPTS OF PEOPLE BECOMING DISORIENTED INSIDE OF A MIN AND ENTERING A DEATH SPIRAL. I DID NOT WANT TO RISK SUCH AN EVENTUALITY; SO RESORTED TO THE 'BENIGN SPIRAL MODE;' A MANEUVER THE MANUFACTURER OF THIS MODEL OF GLIDER RECOMMENDS AS A MEANS TO MAKE A STABILIZED DESCENT WITHOUT TOUCHING THE CTLS. THIS MANEUVER CALLS FOR THE PLT TO PULL THE TRIM FULL AFT AND TO PULL ON FULL SPOILERS; THEN ALLOW THE GLIDER TO DESCEND WITHOUT TOUCHING THE CTLS. THE GLIDER DESCENDED IN A BENIGN SPIRAL FOR A LITTLE OVER 5 MINS; BREAKING OUT BELOW THE CLOUDS AT ABOUT 11000 FT MSL (APPROX 6500 FT AGL). I KNEW IN ADVANCE THAT CLOUD BASE WAS SUFFICIENTLY HIGH THAT WE WOULD BREAK OUT WELL ABOVE THE GND. IN RETROSPECT I SHOULD HAVE PAID MORE ATTENTION TO THE POS OF THE AIRPLANE RELATIVE TO THE STATIONARY CLOUD BEHIND ME; AS I BELIEVE THE WIND SPEED INCREASED DURING OUR HOLD BELOW FL180. I SHOULD ALSO HAVE ENCOURAGED THE STUDENT PLT TO FLY FURTHER OUT INTO THE GAP BETWEEN THE STATIONARY CLOUDS; AN UPWIND MOVE THAT WOULD HAVE KEPT US FURTHER FROM THE CLOUD BEHIND US. I HAVE INCORPORATED THESE TECHNIQUES INTO SUBSEQUENT FLT PRACTICE.

Data retrieved from NASA's ASRS site as of January 2009 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.