B737-800 suffers unreliable first officer pitot static indications in icing conditions at cruise. De...

Attributes
ACN	783333
Time
Date	200804
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 36000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	cruise : level ground : maintenance
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 240 flight time type : 600
ASRS Report	783333
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 177 flight time type : 6600
ASRS Report	783334
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	aircraft equipment other aircraft equipment : eicas a/s slap disagree message other flight crewa other flight crewb
Resolutory Action	aircraft : equipment problem dissipated flight crew : exited adverse environment
Supplementary
Problem Areas	Weather Aircraft Environmental Factor Flight Crew Human Performance
Primary Problem	Aircraft

Narrative:

Flight to ZZZ west of abc VOR cruising at FL360. First officer's airspeed started to decrease; followed by 'unreliable airspeed' indication below airspeed indicator. Then 'altitude disagree' indication below altimeter. Captain's altimeter read FL357. First officer's altimeter remained at FL360. We crosschecked with HUD and determined that captain's altimeter and airspeed indicator were reading correctly. We requested lower to exit rvsm airspace. We were initially cleared to FL330. Upon leveling at FL330; hand flying; the aircraft was difficult to level off. We requested lower and received clearance for lower when we were slightly below FL330 and then given clearance to FL280. We xferred controls to the captain and selected autoplt 'a' since the captain's instruments were giving correct information; then proceeded to complete the QRH items for 'unreliable airspeed; altitude disagreement; and eec alternate mode.' conferred with dispatch and maintenance and continued flight to ZZZ at FL280 without further incident. First officer's airspds and altimeter slowly resumed indicating correct information after exiting IMC. This event; we think; was caused by ice accumulating on the pitot probes on the first officer side. Since probe heat was on at the time; this incident should not have occurred.

Original NASA ASRS Text

Title: B737-800 SUFFERS UNRELIABLE FO PITOT STATIC INDICATIONS IN ICING CONDITIONS AT CRUISE. DESCEND OUT OF RVSM AND EVENTUALLY REGAIN CORRECT INDICATIONS.

Narrative: FLT TO ZZZ W OF ABC VOR CRUISING AT FL360. FO'S AIRSPD STARTED TO DECREASE; FOLLOWED BY 'UNRELIABLE AIRSPD' INDICATION BELOW AIRSPD INDICATOR. THEN 'ALT DISAGREE' INDICATION BELOW ALTIMETER. CAPT'S ALTIMETER READ FL357. FO'S ALTIMETER REMAINED AT FL360. WE XCHKED WITH HUD AND DETERMINED THAT CAPT'S ALTIMETER AND AIRSPD INDICATOR WERE READING CORRECTLY. WE REQUESTED LOWER TO EXIT RVSM AIRSPACE. WE WERE INITIALLY CLRED TO FL330. UPON LEVELING AT FL330; HAND FLYING; THE ACFT WAS DIFFICULT TO LEVEL OFF. WE REQUESTED LOWER AND RECEIVED CLRNC FOR LOWER WHEN WE WERE SLIGHTLY BELOW FL330 AND THEN GIVEN CLRNC TO FL280. WE XFERRED CTLS TO THE CAPT AND SELECTED AUTOPLT 'A' SINCE THE CAPT'S INSTS WERE GIVING CORRECT INFO; THEN PROCEEDED TO COMPLETE THE QRH ITEMS FOR 'UNRELIABLE AIRSPD; ALT DISAGREEMENT; AND EEC ALTERNATE MODE.' CONFERRED WITH DISPATCH AND MAINT AND CONTINUED FLT TO ZZZ AT FL280 WITHOUT FURTHER INCIDENT. FO'S AIRSPDS AND ALTIMETER SLOWLY RESUMED INDICATING CORRECT INFO AFTER EXITING IMC. THIS EVENT; WE THINK; WAS CAUSED BY ICE ACCUMULATING ON THE PITOT PROBES ON THE FO SIDE. SINCE PROBE HEAT WAS ON AT THE TIME; THIS INCIDENT SHOULD NOT HAVE OCCURRED.

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

B737-800 suffers unreliable first officer pitot static indications in icing conditions at cruise. Descend out of rvsm and eventually regain correct indications.