Date: 201201
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: Marginal
Aircraft: B737-400
Operator: Air Carrier
Operating under: Part 121
Flight plan: VFR
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Check Pilot; Pilot Not Flying; Captain
Anomaly: Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action
Contributing factors: Human Factors; Procedure; Weather
Primary problem: Weather

Narrative: This IOE training flight was planned VFR with adequate weather and visibility. Message was received from Dispatch that destination was good VFR. Procedures were reviewed. FMC programmed for RNAV route to provide situational awareness enroute. After departure precipitation along the route was variable and started to reduce visibility to around 5 miles. Our cruising altitude was planned at 1;500 AGL. About midway through the flight where islands make the channel narrow; we received a 'caution terrain' warning - this was also at a point where precipitation had increased and further reduced visibility. Pilot flying made the decision to accomplish terrain avoidance procedure - maximum power/pitch into IMC around the time terrain alerts were received. Our course and heading kept us in the mid point of terrain along the channel. We climbed to around 10;000 FT and received a 'pop-up' IFR clearance from Center to 6;000 MSL and cleared to the RNAV approach. The approach was setup and briefed and the remainder of the flight was accomplished uneventfully.


Second narrative: Weather was reported above the minimums required per the VFR requirements at both the departure and arrival airports. Visibility was noted to be adequate up the channel during the approach on the previous leg. During taxi out the visibility up the channel was noted to have deteriorated slightly; but a message was received from Dispatch indicating that although there was light snow at destination; the visibility was still good enough for the VFR leg. A normal departure was accomplished; a VFR flightplan was opened; and the VFR leg was conducted down the channel. At the narrowest portion in the channel at approximately 1;500 FT it began snowing; severely reducing visibility. Although the channel was still barely visible the decision was made to initiate a maximum performance climb into IMC conditions in response to a ground proximity 'terrain' warning. Ground proximity 'terrain' warnings are occasionally experienced while maneuvering on VFR routes. The reduced visibility AND 'terrain' warning together left a question as to our absolute ability to see and avoid the terrain. The safest course of action was to climb in IMC; aligning the aircraft with the magenta line for the IFR route. After initiating the climb on the channel [we were] heading to a safe altitude (10;000 FT) and then requesting an IFR clearance. A clearance was requested; and received; from Center to descend to 6;000 FT. After one turn in the hold the RNAV approach was flown to landing. A BE1900 flew the route VFR right after we landed without incident.


Synopsis: Air Carrier flight crew reports entering IMC and receiving a GPWS terrain warning while at low altitude on a VFR flight plan. An immediate climb is initiated and ATC is contacted for an IFR clearance. An RNAV approach at destination ensues.