Small aircraft twin at high altitude gets involved with thunderstorms, icing and vertical drafts, ha...

Attributes
ACN	150321
Time
Date	199007
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : drk
State Reference	AZ
Altitude	msl bound lower : 21900 msl bound upper : 24000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zab
Operator	general aviation : personal
Make Model Name	Small Transport, Low Wing, 2 Recip Eng
Flight Phase	climbout : intermediate altitude cruise other cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : cfi pilot : instrument pilot : commercial
Experience	flight time last 90 days : 100 flight time total : 6000 flight time type : 150
ASRS Report	150321
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather inflight encounter other non adherence : clearance other anomaly other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : regained aircraft control other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation other

Narrative:

Began westbound flight from saf. Briefed for occasional scattered to isolated thunderstorms, ceiling 7000-8000' AGL. On climb out could not see acceptable terrain clearance westbound below clouds, so climbed VFR to 16500'. After about 40 mi cloud deck ahead was rising, so I requested and got FL220 from ZAB. Clearance direct gup direct drk direct sez, with deviations approved as necessary to avoid buildups. Used stormscope and visibility sighting of thunderstorm to avoid them. At approximately location noted above rising tops led to a request (center approval) for FL240. Nearing top of climb encountered a cloud which had violent up and downdrafts and considerable precipitation noise. The aircraft picked up about 3/8 of jagged rime on the wings. As I reduced pitch to level at FL240, the aircraft began vibrating and porpoising up and down about 180' and a few seconds at 120 KIAS (stall speed 72 KIAS). Aircraft was certified known icing and all heat systems were on. A sudden downdraft was encountered, which made it impossible to hold altitude. I called center twice (answered second time), informing controller I was unable to maintain FL240. I was then cleared down to FL220, still in downdraft. I was able to stabilize aircraft at FL219, then regain to FL220. The ice started to come off at FL255, indicated temperature at this altitude an unbelievable +5 degrees C. Rest of flight uneventful. This is the strangest behavior I've seen in this aircraft. I thought at first I had encountered prestall buffet, but the aircraft's gaining altitude while porpoising argues against this. So does other aircraft behavior (i.e., full aileron control). Nothing strange on post-flight inspection. Descent was finally arrested by deciding aircraft was not stalled and increasing pitch with no further buffeting, porpoising, etc. I can only wonder if odd form ice load was shaking the elevator or acting as a spoiler.

Original NASA ASRS Text

Title: SMA TWIN AT HIGH ALT GETS INVOLVED WITH TSTMS, ICING AND VERTICAL DRAFTS, HAS TEMPORARY LOSS OF ACFT CTL AND GETS A LOWER ALT AS HE EXPERIENCES ALT DEVIATIONS.

Narrative: BEGAN WBND FLT FROM SAF. BRIEFED FOR OCCASIONAL SCATTERED TO ISOLATED TSTMS, CEILING 7000-8000' AGL. ON CLBOUT COULD NOT SEE ACCEPTABLE TERRAIN CLRNC WBND BELOW CLOUDS, SO CLBED VFR TO 16500'. AFTER ABOUT 40 MI CLOUD DECK AHEAD WAS RISING, SO I REQUESTED AND GOT FL220 FROM ZAB. CLRNC DIRECT GUP DIRECT DRK DIRECT SEZ, WITH DEVIATIONS APPROVED AS NECESSARY TO AVOID BUILDUPS. USED STORMSCOPE AND VIS SIGHTING OF TSTM TO AVOID THEM. AT APPROX LOCATION NOTED ABOVE RISING TOPS LED TO A REQUEST (CENTER APPROVAL) FOR FL240. NEARING TOP OF CLB ENCOUNTERED A CLOUD WHICH HAD VIOLENT UP AND DOWNDRAFTS AND CONSIDERABLE PRECIPITATION NOISE. THE ACFT PICKED UP ABOUT 3/8 OF JAGGED RIME ON THE WINGS. AS I REDUCED PITCH TO LEVEL AT FL240, THE ACFT BEGAN VIBRATING AND PORPOISING UP AND DOWN ABOUT 180' AND A FEW SECS AT 120 KIAS (STALL SPD 72 KIAS). ACFT WAS CERTIFIED KNOWN ICING AND ALL HEAT SYSTEMS WERE ON. A SUDDEN DOWNDRAFT WAS ENCOUNTERED, WHICH MADE IT IMPOSSIBLE TO HOLD ALT. I CALLED CENTER TWICE (ANSWERED SECOND TIME), INFORMING CTLR I WAS UNABLE TO MAINTAIN FL240. I WAS THEN CLRED DOWN TO FL220, STILL IN DOWNDRAFT. I WAS ABLE TO STABILIZE ACFT AT FL219, THEN REGAIN TO FL220. THE ICE STARTED TO COME OFF AT FL255, INDICATED TEMP AT THIS ALT AN UNBELIEVABLE +5 DEGS C. REST OF FLT UNEVENTFUL. THIS IS THE STRANGEST BEHAVIOR I'VE SEEN IN THIS ACFT. I THOUGHT AT FIRST I HAD ENCOUNTERED PRESTALL BUFFET, BUT THE ACFT'S GAINING ALT WHILE PORPOISING ARGUES AGAINST THIS. SO DOES OTHER ACFT BEHAVIOR (I.E., FULL AILERON CTL). NOTHING STRANGE ON POST-FLT INSPECTION. DSNT WAS FINALLY ARRESTED BY DECIDING ACFT WAS NOT STALLED AND INCREASING PITCH WITH NO FURTHER BUFFETING, PORPOISING, ETC. I CAN ONLY WONDER IF ODD FORM ICE LOAD WAS SHAKING THE ELEVATOR OR ACTING AS A SPOILER.

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.

Small aircraft twin at high altitude gets involved with thunderstorms, icing and vertical drafts, has temporary loss of aircraft control and gets a lower altitude as he experiences altitude deviations.