A B737-300 encountered a plastic bag or sheet on takeoff roll which covered the captain's pitot prob...

Attributes
ACN	354625
Time
Date	199612
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : zzz
State Reference	US
Altitude	agl bound lower : 0 agl bound upper : 0
Environment
Light	Night
Aircraft 1
Controlling Facilities	tower : zzz tower : rsw
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	climbout : takeoff other
Route In Use	departure other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	other personnel other
Qualification	other other : other
ASRS Report	354625
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other flight crewa other other : unspecified cockpit
Resolutory Action	other
Consequence	Other
Supplementary
Air Traffic Incident	other

Narrative:

On takeoff out of ZZZ aircraft encountered an airspeed split between the captain's and first officer's airspeed indicators. The split was approximately 40 KTS. Shortly after the discrepancy was encountered it corrected itself. The flight crew elected to return to ZZZ as a precaution, even though airspeed indicator functioned properly for remainder of flight. Upon arrival in ZZZ, maintenance inspected the pitot static ports and found what looked like a piece of plastic melted on the captain's pitot probe. Then maintenance removed the piece of plastic from the side of the pitot probe and did a bite test of the CADC system. The system bite check was good. A research of history in air traffic area 3400 showed no prior discrepancies. It was surmised that a piece of plastic was caught on the pitot tube while the aircraft was either at the gate or on taxi out for takeoff. It melted onto the probe when pitot heat was turned on. After aircraft rotated and began its climb the force of the airflow past the probe must have dislodged the plastic, thus returning the airspeed indication to normal. Loose debris at airport is the suspected cause.

Original NASA ASRS Text

Title: A B737-300 ENCOUNTERED A PLASTIC BAG OR SHEET ON TKOF ROLL WHICH COVERED THE CAPT'S PITOT PROBE CAUSING A 40 KT AIRSPD ERROR. ACFT RETURNED TO THE FIELD.

Narrative: ON TKOF OUT OF ZZZ ACFT ENCOUNTERED AN AIRSPD SPLIT BTWN THE CAPT'S AND FO'S AIRSPD INDICATORS. THE SPLIT WAS APPROX 40 KTS. SHORTLY AFTER THE DISCREPANCY WAS ENCOUNTERED IT CORRECTED ITSELF. THE FLC ELECTED TO RETURN TO ZZZ AS A PRECAUTION, EVEN THOUGH AIRSPD INDICATOR FUNCTIONED PROPERLY FOR REMAINDER OF FLT. UPON ARR IN ZZZ, MAINT INSPECTED THE PITOT STATIC PORTS AND FOUND WHAT LOOKED LIKE A PIECE OF PLASTIC MELTED ON THE CAPT'S PITOT PROBE. THEN MAINT REMOVED THE PIECE OF PLASTIC FROM THE SIDE OF THE PITOT PROBE AND DID A BITE TEST OF THE CADC SYS. THE SYS BITE CHK WAS GOOD. A RESEARCH OF HISTORY IN ATA 3400 SHOWED NO PRIOR DISCREPANCIES. IT WAS SURMISED THAT A PIECE OF PLASTIC WAS CAUGHT ON THE PITOT TUBE WHILE THE ACFT WAS EITHER AT THE GATE OR ON TAXI OUT FOR TKOF. IT MELTED ONTO THE PROBE WHEN PITOT HEAT WAS TURNED ON. AFTER ACFT ROTATED AND BEGAN ITS CLB THE FORCE OF THE AIRFLOW PAST THE PROBE MUST HAVE DISLODGED THE PLASTIC, THUS RETURNING THE AIRSPD INDICATION TO NORMAL. LOOSE DEBRIS AT ARPT IS THE SUSPECTED CAUSE.

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.

A B737-300 encountered a plastic bag or sheet on takeoff roll which covered the captain's pitot probe causing a 40 KT airspeed error. Aircraft returned to the field.