While climbing over the western pacific between 16;000 feet and FL260 with thunderstorms in the area...

Narrative:

Climb out from a pacific island; numerous thunderstorms in area and extensive deviation from route. On climb out of 16;000 captain's (ca) altimeter jumped from 16;000 to FL180 and then jumped again down to 14;000 before settling back around FL185; after this I asked the first officer (first officer) if he had seen the same thing which he said he did. I then asked if he had noticed his altimeter doing the same to which he said no and he did not think the standby had either. We discussed continuing if we did not observe this again; but before we had even finished looking through the QRH to see if there was anything about this type of incident it happened again going through FL260. This time we both verified that the first officer and standby had not been effected; and immediately transferred control from the ca to the first officer.I got on the sat phone and called dispatch advising them of the issue and asking for a three way patch to maintenance; after getting the patch and explaining to the mechanic what we had experienced we all agreed that taking this aircraft to our island destination into known mountainous terrain at night and in weather would not be a good idea. Maintenance asked my weight and advised burning fuel before landing in departure airport; the dispatcher concurred and so we orbited for an hour plus to burn off enough to be below max landing weight. Uneventful approach and landing.

Original NASA ASRS Text

Title: While climbing over the Western Pacific between 16;000 feet and FL260 with thunderstorms in the area; a B737 Captain's altimeter was intermittently fluctuating so the flight returned to the departure airport on the advice of Maintenance.

Narrative: Climb out from a Pacific Island; numerous thunderstorms in area and extensive deviation from route. On climb out of 16;000 Captain's (CA) altimeter jumped from 16;000 to FL180 and then jumped again down to 14;000 before settling back around FL185; after this I asked the First Officer (FO) if he had seen the same thing which he said he did. I then asked if he had noticed his altimeter doing the same to which he said no and he did not think the standby had either. We discussed continuing if we did not observe this again; but before we had even finished looking through the QRH to see if there was anything about this type of incident it happened again going through FL260. This time we both verified that the FO and standby had not been effected; and immediately transferred control from the CA to the FO.I got on the SAT phone and called dispatch advising them of the issue and asking for a three way patch to maintenance; after getting the patch and explaining to the Mechanic what we had experienced we all agreed that taking this aircraft to our island destination into known mountainous terrain at night and in weather would not be a good idea. Maintenance asked my weight and advised burning fuel before landing in departure airport; the Dispatcher concurred and so we orbited for an hour plus to burn off enough to be below max landing weight. Uneventful approach and landing.

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.

Attributes
ACN	1290445
Time
Date	201508
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	IMC
Light	Dusk
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Climb
Route In Use	Oceanic
Flight Plan	IFR
Component
Aircraft Component	Pitot/Static Ice System
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 64 Flight Crew Type 311
Events
Anomaly	Aircraft Equipment Problem Critical Inflight Event / Encounter Weather / Turbulence

While climbing over the western pacific between 16;000 feet and FL260 with thunderstorms in the area; a B737 captain's altimeter was intermittently fluctuating so the flight returned to the departure airport on the advice of maintenance.