Enroute Controller described a loss of separation event when an aircraft was unable to maintain assigned altitude due to weather.
Synopsis
Enroute Controller described a loss of separation event when an aircraft was unable to maintain assigned altitude due to weather.
Narrative
There was weather in the sector about 15 miles in diameter and no aircraft were going through it. All westbound aircraft entered the sector deviating left. Midway arrivals; which usually go though another sector; were being rerouted through our sector because of this line of weather; they were entering the sector at 17;000 FT; 250 KTS; and also deviating to the left when able direct to the next fix. Aircraft X entered the sector at 16;000 FT; westbound deviating to the left; Aircraft Y entered the sector at 17;000 FT and was deviating left. Aircraft X began turning just south of Aircraft Y. Once they were within 5 miles of Aircraft Y; aircraft 1 showed 3;000 FT above the assigned altitude. The R-Side Controller caught this right away and stated to Aircraft X they were showing 3;000 above altitude and to confirm they were level at 16;000 FT. Aircraft X did not respond to the Controller. Then the aircraft showed at 16;500 FT. At that point; the RADAR Controller restated to the aircraft they were now showing 500 FT above altitude and to confirm they were level at 16;000 FT. Aircraft X finally responded and stated they were descending back to 16;000 FT. At this point the aircraft were about 3 miles apart; Aircraft X headed northwest bound and Aircraft Y still deviating left of course; westbound. After about a minute; Aircraft X reported they were in a bad cloud with hail and the conditions that got really bad. The RADAR Controller then told the aircraft next time they had to tell the Controller if they were not able to hold altitude and that an aircraft was right above them at 17;000 FT. The only recommendation would be that the RADAR Controller should have called traffic for the two aircraft. But they were not traffic until Aircraft X turned. I do not believe the RADAR Controller realized the aircraft began to turn back and the Aircraft X did not state this to the Controller.
Second reporter narrative
While in cruise deviating around weather; suddenly entered an area of strong updrafts; turbulence; and precipitation including hail. Autopilot was coupled but did not hold altitude. I disconnected the autopilot; and pulled the throttles to zero thrust. Strong updrafts still took the airplane up 500 FT before altitude control could be regained. The entire event lasted less than half a minute. Altitude deviation caused loss of separation with another jet at 17;000 FT.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.