A B777 deviated from their assigned route because of weather at FL410 in foreign airspace; unable to contact ATC. During the deviation a 20 degree temperature rise resulted in an airspeed loss and a requirement to descend for airspeed control.
Synopsis
A B777 deviated from their assigned route because of weather at FL410 in foreign airspace; unable to contact ATC. During the deviation a 20 degree temperature rise resulted in an airspeed loss and a requirement to descend for airspeed control.
Narrative
While deviating around a quickly developing thunderstorm cell; speed was gradually slowing from mach 82 to 15 KTS above amber bar. The TAT at FL410 was -26C before and after the event with a FMC maximum altitude of FL423. Downwind of the cell; the TAT climbed to -6C with a corresponding maximum altitude of FL403. To maintain minimum speed a descent of 200-300 FPM was required. Concurrent with the performance degradation; the left EEC went inoperative; slightly lowering the thrust limit to the left engine. At FL400 the aircraft began to climb back to FL410 at about 500 FPM. The excursion from clearance altitude lasted under five minutes. Our position during the altitude deviation was 20-30 miles east of the airway. There were no other aircraft on frequency or on our TCAS display. The radio had a lot of static; and continuous attempts were made to contact Center. We were uncertain if they heard or understood us; but we continued to state our circumstance and intentions in the blind; even on 121.5. Once around the weather all conditions returned to normal; communications were regained; and the flight continued normally. No declarations or reports to ATC were made and none were requested. Both the First Officer's radio and the EEC were entered into the Maintenance Log for repair.
Second reporter narrative
I had just returned to the cockpit after taking the third break; it was approximately one hour prior to landing. I noticed we were at FL410 and deviated east of course due to thunderstorms ahead. As we approached the line of thunderstorms it became obvious we would need to deviate further east to remain clear of them. I attempted to contact ATC for clearance to deviate. ATC was very weak with a lot of static on the radio. They were talking to other aircraft in different languages and would not reply to my request to deviate. We continued to deviate further east of course without a clearance. When I was finally able to get ATC to talk to me; we were told to contact the next sector and were given a primary and secondary frequency. By this time we were well within that sector's airspace. I tried numerous times to contact ATC on both frequencies and 121.5 without receiving any reply. During this time I was also monitoring the thunderstorms and our position. I noticed the airspeed was decaying toward the yellow foot and mentioned it to the Captain. He said he was going to need a lower altitude; it was then I noticed the throttles were full forward and we were on the backside of the power curve. As we began a descent; I monitored TCAS and continued to try and contact ATC without any luck. I believe we descended about 2000 FT before we were able to start a climb back to FL410. After we were level at FL410 we corrected back to course. I switched ATC frequency back to the assigned frequency and was handed off to the next sector. ATC made no mention of our deviation and neither did we.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.