A B767 captain reported that at FL360 in cruise both altimeter systems fluctuated independently in t...

Attributes
ACN	1141549
Time
Date	201401
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	B767 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	IFR
Component
Aircraft Component	Pitot-Static System
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Engineer Flight Crew Flight Instructor Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 90 Flight Crew Total 10500 Flight Crew Type 5000
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy Inflight Event / Encounter Weather / Turbulence

Narrative:

About 30 minutes after reaching cruise altitude; captain and first officer altimeters fluctuated as I've never seen in 23 years of flying this aircraft. The fluctuations were on the order of 20-60 feet most of the time; but at times it was 100-200 feet. The fluctuations were very rapid and directly proportional to turbulence intensity; the greater the turbulence intensity; the greater the fluctuation. The standby altimeter fluctuated 20-30 feet. The captain and first officer altimeters fluctuated independently.we were in rvsm airspace; but I was never in doubt that we were precisely maintaining our assigned altitude. The autoflight at no time 'chased' the altitude fluctuations. Our altitude relative to TCAS targets was as expected and ATC never queried our altitude. Before our flight; the aircraft was parked for several hours in a heavy blowing rain. It is possible that water incursion into the static ports may be a factor.

Original NASA ASRS Text

Title: A B767 Captain reported that at FL360 in cruise both altimeter systems fluctuated independently in turbulence up to 200 FT after the aircraft was previously parked in heavy blowing rain for several hours. The aircraft remained stable during the repeated altimeter excursions.

Narrative: About 30 minutes after reaching cruise altitude; Captain and First Officer altimeters fluctuated as I've never seen in 23 years of flying this aircraft. The fluctuations were on the order of 20-60 feet most of the time; but at times it was 100-200 feet. The fluctuations were very rapid and directly proportional to turbulence intensity; the greater the turbulence intensity; the greater the fluctuation. The standby altimeter fluctuated 20-30 feet. The Captain and First Officer altimeters fluctuated independently.We were in RVSM airspace; but I was never in doubt that we were precisely maintaining our assigned altitude. The autoflight at no time 'chased' the altitude fluctuations. Our altitude relative to TCAS targets was as expected and ATC never queried our altitude. Before our flight; the aircraft was parked for several hours in a heavy blowing rain. It is possible that water incursion into the static ports may be a factor.

Data retrieved from NASA's ASRS site 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 B767 captain reported that at FL360 in cruise both altimeter systems fluctuated independently in turbulence up to 200 ft after the aircraft was previously parked in heavy blowing rain for several hours. The aircraft remained stable during the repeated altimeter excursions.