B767-300 and 300 ER
Flight Crew Air Transport Pilot (ATP)
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Procedure; Weather
Approaching SOORY on NAT track; we were given two SIGMETS by Commercial Radio concerning thunderstorms. The areas were plotted on our chart showing our cleared track in the center of the area. Between SOORY and 44N50W we detected severe weather on our track. We requested deviation from track 90 miles from the storm. At 30 miles from the thunderstorm we started a deviation to stay clear of weather. Approximately 10 miles left of track we received a SELCAL relaying ATC message 'unable deviation'. I informed ATC that I was exercising Captain's emergency authority and we would descend 300 FT. All part 1 and North Atlantic orientation chart procedures were followed and we twice relayed new estimates for the next fix. In spite of having Pegasus aircraft with data link we never received Sigmets from Dispatch. We copied entire Sigmets via HF. It would be useful to have a printed copy of Sigmets instead of writing them in turbulence at night from a fast talking radio operator. It would also reduce frequency congestion if we could answer affirmative when asked if we have Sigmet XXX. Nowhere could I find that it is required to declare an emergency in this circumstance. It would be helpful if are manual could address this issue.
I was the Relief Pilot on this flight; I was just coming off my crew break. Before I sat down to fly the aircraft I notice on radar a very large Thunderstorm on our flight path. Approaching SOORY on NAT track; we were given two SIGMETS by Commercial Radio concerning thunderstorms. The areas were plotted on our chart showing our cleared track in the center of the area. Between SOORY and 44N50W we detected severe weather on our track. We requested deviation from track 90 miles from the storm. At 30 miles from the thunderstorm we started a deviation to stay clear of weather. Approximately 10 miles left of track we received a SELCAL relaying ATC message 'unable deviation'. I informed ATC that I was exercising Captain's emergency authority and we would descend 300 FT.
B767 flight crew reports deviating around a thunderstorm on a North Atlantic Track using Captain's emergency authority when ATC cannot provide a clearance to do so.