Enroute controller described a loss of separation event when a military fighter initiated an unexpec...

Narrative:

An F15 [was] climbing from FL410 to FL450. Told me he could not hold altitude. I re-cleared him to FL390. He descended through FL390 and kept descending without telling me. I asked him his altitude. He told me he couldn't maintain altitude. I asked him what he needed to descend to. He said FL250. He also lost all speed of the aircraft. Another aircraft was initially 10 miles behind him at 450 KTS climbing up to FL430. The second aircraft was overtaking the first rapidly. I turned the aircraft 90 degrees to the right to try and keep 5 mile separation. They passed with about 4 miles of separation. All this happened with heavy traffic volume and high complexity due to weather. If I hadn't been so busy I could have quizzed the F15 more about the problem. This would have led to a quicker realization of the potential problem of loss of separation due to loss of altitude and loss of speed. Or if the F15 had told me how bad the problem was; or declared an emergency; I would have turned the aircraft sooner. Military aircraft should declare an emergency when they cannot hold altitude and/or maintain speed.

Original NASA ASRS Text

Title: Enroute Controller described a loss of separation event when a military fighter initiated an unexpected descent due to aircraft problems without informing ATC of details. The reporter indicated that the aircraft should have declared an emergency.

Narrative: An F15 [was] climbing from FL410 to FL450. Told me he could not hold altitude. I re-cleared him to FL390. He descended through FL390 and kept descending without telling me. I asked him his altitude. He told me he couldn't maintain altitude. I asked him what he needed to descend to. He said FL250. He also lost all speed of the aircraft. Another aircraft was initially 10 miles behind him at 450 KTS climbing up to FL430. The second aircraft was overtaking the first rapidly. I turned the aircraft 90 degrees to the right to try and keep 5 mile separation. They passed with about 4 miles of separation. All this happened with heavy traffic volume and high complexity due to weather. If I hadn't been so busy I could have quizzed the F15 more about the problem. This would have led to a quicker realization of the potential problem of loss of separation due to loss of altitude and loss of speed. Or if the F15 had told me how bad the problem was; or declared an emergency; I would have turned the aircraft sooner. Military aircraft should declare an emergency when they cannot hold altitude and/or maintain speed.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	995542
Time
Date	201202
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Aircraft 1
Make Model Name	Eagle (F-15)
Operating Under FAR Part	Part 91
Flight Phase	Climb
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	Climb
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Altitude Excursion From Assigned Altitude Deviation - Speed All Types

Enroute controller described a loss of separation event when a military fighter initiated an unexpected descent due to aircraft problems without informing ATC of details. The reporter indicated that the aircraft should have declared an emergency.