Flight instructor deviated from assigned track and altitude during a dual instrument training cross country flight because of aircraft pitot tube icing causing loss of the airspeed indicator in IMC.

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Attributes
ACN	237381
Time
Date	199303
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : tfd
State Reference	AZ
Altitude	msl bound lower : 7000 msl bound upper : 9000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Operator	general aviation : instructional
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Retractable Gear
Flight Phase	cruise other descent other other
Route In Use	enroute airway : v105
Flight Plan	IFR
Person 1
Affiliation	Other
Function	instruction : instructor
Qualification	pilot : instrument pilot : cfi pilot : commercial
Experience	flight time last 90 days : 40 flight time total : 575 flight time type : 45
ASRS Report	237381
Person 2
Affiliation	Other
Function	instruction : trainee
Qualification	pilot : private
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance other spatial deviation
Independent Detector	atc equipment other atc equipment : unspecified other controllera other flight crewa
Resolutory Action	flight crew : exited adverse environment
Consequence	faa : reviewed incident with flight crew faa : investigated
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

IFR dual cross country with private student. We were in IMC and lost airspeed indicator. Airspeed first increased then dropped to zero. Student did not recognize and tried to increase airspeed by pitching down. I took over and elected to descend 2000 ft into known VMC. I also turned off the airway 90 degrees so I would not descend into any possible traffic. My decision to descend was based on the chance of ice in the pitot tube. ATC was upset about a deviation (possible action) without a clearance or declaring an emergency. I felt there was not enough time, until the situation was fully under control. As PIC, I feel it was allowable under part 91.3 for my command decision, the FAA may take very serious action.

Original NASA ASRS Text

Title: FLT INSTRUCTOR DEVIATED FROM ASSIGNED TRACK AND ALT DURING A DUAL INST TRAINING XCOUNTRY FLT BECAUSE OF ACFT PITOT TUBE ICING CAUSING LOSS OF THE AIRSPD INDICATOR IN IMC.

Narrative: IFR DUAL XCOUNTRY WITH PVT STUDENT. WE WERE IN IMC AND LOST AIRSPD INDICATOR. AIRSPD FIRST INCREASED THEN DROPPED TO ZERO. STUDENT DID NOT RECOGNIZE AND TRIED TO INCREASE AIRSPD BY PITCHING DOWN. I TOOK OVER AND ELECTED TO DSND 2000 FT INTO KNOWN VMC. I ALSO TURNED OFF THE AIRWAY 90 DEGS SO I WOULD NOT DSND INTO ANY POSSIBLE TFC. MY DECISION TO DSND WAS BASED ON THE CHANCE OF ICE IN THE PITOT TUBE. ATC WAS UPSET ABOUT A DEV (POSSIBLE ACTION) WITHOUT A CLRNC OR DECLARING AN EMER. I FELT THERE WAS NOT ENOUGH TIME, UNTIL THE SIT WAS FULLY UNDER CTL. AS PIC, I FEEL IT WAS ALLOWABLE UNDER PART 91.3 FOR MY COMMAND DECISION, THE FAA MAY TAKE VERY SERIOUS ACTION.

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.