<< >> NASA ASRS Report 128627, November 1989

Pilot of light twin engine aircraft missets altimeter during period of rapid barometric pressure change. Altitude deviation from assigned altitude occurs.

Attributes
ACN	128627
Time
Date	198911
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ewo
State Reference	KY
Altitude	msl bound lower : 10500 msl bound upper : 11000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid
Operator	general aviation : personal
Make Model Name	Small Transport
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 15 flight time total : 700 flight time type : 50
ASRS Report	128627
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude inflight encounter : weather inflight encounter other other anomaly other
Independent Detector	other controllera
Resolutory Action	flight crew : became reoriented flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I was on a flight from sav to pia. There was an intense cold front across my route of flight that spawned many thunderstorms and tornadoes. I was about 100 NM southeast of ilu when center broadcast convective SIGMET and tornado watch across my route. I decided to divert to ilu to rechk WX. The barometric pressure dropped from 30.00 at sav to 29.47 at ilu. I misset my altimeter and deviated below my assigned altitude. I think that several factors contributed to the problem: 1) a very rapid change in barometric pressure over a distance of about 100 NM. 2) very high single pilot workload--I had lost an alternator and was bury shedding elect load, deviating around trw, and had my routing revised. The approach I was to expect was changed right before starting the approach.

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Original NASA ASRS Text

Title: PLT OF LIGHT TWIN ENGINE ACFT MISSETS ALTIMETER DURING PERIOD OF RAPID BAROMETRIC PRESSURE CHANGE. ALT DEVIATION FROM ASSIGNED ALT OCCURS.

Narrative: I WAS ON A FLT FROM SAV TO PIA. THERE WAS AN INTENSE COLD FRONT ACROSS MY ROUTE OF FLT THAT SPAWNED MANY TSTMS AND TORNADOES. I WAS ABOUT 100 NM SE OF ILU WHEN CENTER BROADCAST CONVECTIVE SIGMET AND TORNADO WATCH ACROSS MY ROUTE. I DECIDED TO DIVERT TO ILU TO RECHK WX. THE BAROMETRIC PRESSURE DROPPED FROM 30.00 AT SAV TO 29.47 AT ILU. I MISSET MY ALTIMETER AND DEVIATED BELOW MY ASSIGNED ALT. I THINK THAT SEVERAL FACTORS CONTRIBUTED TO THE PROB: 1) A VERY RAPID CHANGE IN BAROMETRIC PRESSURE OVER A DISTANCE OF ABOUT 100 NM. 2) VERY HIGH SINGLE PLT WORKLOAD--I HAD LOST AN ALTERNATOR AND WAS BURY SHEDDING ELECT LOAD, DEVIATING AROUND TRW, AND HAD MY ROUTING REVISED. THE APCH I WAS TO EXPECT WAS CHANGED RIGHT BEFORE STARTING THE APCH.

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.