Erroneous altimeter reading and mode C transmission.

Attributes
ACN	128658
Time
Date	198911
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : har
State Reference	PA
Altitude	msl bound lower : 6000 msl bound upper : 7100
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : har
Operator	common carrier : air taxi
Make Model Name	Small Transport
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : instrument
Experience	flight time last 90 days : 75 flight time total : 1670
ASRS Report	128658
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllera other other : unspecified cockpit
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

The day of the 16TH there was heavy rain and thunderstorms associated with the passage of an arctic cold front. So, during my preflight for that evening I opened the 2 static system drains. After not seeing any water/moisture I closed them and finished the preflight. With a normal takeoff and departure I went about the routine of taking a trend during which I recorded an OAT of -12C. I checked in level at 6000 MSL. I noticed a slight drop in airspeed (about 10 KTS) and saw a 3 degree pitch up on the attitude indicator, but the altimeter and vsi did not indicate a climb. Something was wrong, so I deployed the alternate static source at which time the altimeter and mode C read 7100' MSL. I conclude that there was water trapped in the static system that could not drain, and with the -12C temperature frozen in the line blocking the system with 6000 MSL air pressure and so the altimeter would not show the climb nor would the mode C.

Original NASA ASRS Text

Title: ERRONEOUS ALTIMETER READING AND MODE C TRANSMISSION.

Narrative: THE DAY OF THE 16TH THERE WAS HEAVY RAIN AND TSTMS ASSOCIATED WITH THE PASSAGE OF AN ARCTIC COLD FRONT. SO, DURING MY PREFLT FOR THAT EVENING I OPENED THE 2 STATIC SYSTEM DRAINS. AFTER NOT SEEING ANY WATER/MOISTURE I CLOSED THEM AND FINISHED THE PREFLT. WITH A NORMAL TKOF AND DEP I WENT ABOUT THE ROUTINE OF TAKING A TREND DURING WHICH I RECORDED AN OAT OF -12C. I CHECKED IN LEVEL AT 6000 MSL. I NOTICED A SLIGHT DROP IN AIRSPEED (ABOUT 10 KTS) AND SAW A 3 DEG PITCH UP ON THE ATTITUDE INDICATOR, BUT THE ALTIMETER AND VSI DID NOT INDICATE A CLIMB. SOMETHING WAS WRONG, SO I DEPLOYED THE ALTERNATE STATIC SOURCE AT WHICH TIME THE ALTIMETER AND MODE C READ 7100' MSL. I CONCLUDE THAT THERE WAS WATER TRAPPED IN THE STATIC SYSTEM THAT COULD NOT DRAIN, AND WITH THE -12C TEMPERATURE FROZEN IN THE LINE BLOCKING THE SYSTEM WITH 6000 MSL AIR PRESSURE AND SO THE ALTIMETER WOULD NOT SHOW THE CLIMB NOR WOULD THE MODE C.

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