B747 flight crew describes the use of CPDLC to request deviations around convective weather in the central pacific. An emergency is declared when further deviation is required prior to receiving a second clearance via CPDLC.
Synopsis
B747 flight crew describes the use of CPDLC to request deviations around convective weather in the central pacific. An emergency is declared when further deviation is required prior to receiving a second clearance via CPDLC.
Narrative
Flight under CPDLC [Controller Pilot Data Link Communication]. When I was awakened from crew rest for over water crew change; I took F/O's seat with Captain still in his seat (about to go on break) flying. Crew had already requested and received clearance to deviate left or right of course for an extensive area of convective wx. We agreed clearance insufficient to avoid all echoes; so requested additional latitude; before this clearance could be received the immediate need for additional leeway arose. Declared emergency using CPDLC. Aircraft may or may not have exceeded lateral limits of deviation clearance; am filing this report now just in case it did. Ultimately; ATC asked if we desired a revised clearance; and we responded in the affirmative. Revised clearance obtained; was loaded into FMC; and flight proceeded normally from this point. Turbulence never did quite reach 'Moderate' level; as it turned out. However; seat belt sign was on throughout this encounter and F/A's were seated by PA from cockpit. So far as I recall; flight conducted in accordance with SOP/FAR/etc in all respects.
Second reporter narrative
We were advised by Dispatch and ATC that another aircraft had to deviate several miles around a large area of storms that were in front of us. At FL360; we requested a deviation right of course of 50 NM. ATC cleared us deviate either side of track by 100 NM. We began a deviation right of course toward the upwind side of the storms. We found ourselves flying parallel to a massive area of rapidly building storms. About 25 minutes later we found that a gap in the storms which we were considering using to return to course was closing. We were approaching our maximum deviation limit of 100 NM. We declared an ATC emergency via CPDLC and asked ATC for 150 NM right of course ASAP. ATC immediately cleared us to deviate either side up to 128 NM. They also informed us that 128 NM was the maximum deviation allowed and asked us if we needed a reroute. We requested and received a reroute. Seven minutes later we requested another 30 NM left of the new course. ATC then cleared us to deviate up to 128 NM either side of the new course. I believe all pilots and dispatchers working the Pacific should be made aware of the 128 NM limit and the reroute procedure which allows further deviations. It should also be noted that if we had been required to return to our original route instead of continuing on our reroute; a fuel stop would have been mandatory. Knowledge of the 128 NM limit and a reroute procedure which allows further deviations is a great tool in resolving the very dynamic and changing environment of rapidly building storms.
More incidents for this aircraft family →
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.