Center controller reported a helicopter in an area of no radar coverage and intermittent radio cover...

Narrative:

[Aircraft] was filed on an airway. I climbed them to 11000 ft. When they checked in. I lost radar contact with the aircraft which is a common occurrence due to our radar coverage. I told him radar contact lost and to expect identification soon. He didn't respond. I tried him on my other transmitter. I didn't get anything back. It is also fairly common to not be able to hear aircraft at that altitude in the area. I didn't think much of it. Then a few minutes later; I was shipping an airplane who told me they were hearing an [military] aircraft on guard who said they couldn't maintain altitude and needed vectors to the closest airport. I asked the pilot if the call sign was [aircraft] and they said it was. I told the aircraft to remain on my frequency and immediately began to try and relay through them. I relayed that I had lost [aircraft] on radar and said where the nearest airport was reference their last position before I lost radar.I kept trying to relay through various aircraft; assuming [aircraft] was in an extreme urgency situation. A few minutes later I saw [aircraft] come back up on my radar below the mia in the area. I relayed to an airplane where another nearby airport was. I had an airplane relay to me that the aircraft wanted vectors toward their destination. In lieu of radar-identifying the aircraft through a relay and given the situation I made the judgment to believe that the radar hit correlated with the aircraft in question. I relayed to have them fly a heading toward their destination as requested. At this point; it appeared they began to climb again. I relayed to have them maintain an altitude at the mia; which they were back at. I then tried to talk directly to the aircraft. This worked momentarily; but then I couldn't get them to read anything back. I relayed through another plane that they were radar contact again and to maintain their current heading and altitude. I then relayed a frequency change to approach. I did not ever ask why they couldn't maintain altitude; nor did I try to relay a safety alert. I believed the pilots were in a very; very stressful situation and knew that they were in an unsafe situation. Resultantly; my goal was to give them whatever assistance I could to get them pointed toward their airport of choice.

Original NASA ASRS Text

Title: Center Controller reported a helicopter in an area of no radar coverage and intermittent radio coverage experienced difficulty and descended below the Minimum IFR Altitude.

Narrative: [Aircraft] was filed on an airway. I climbed them to 11000 ft. when they checked in. I lost radar contact with the aircraft which is a common occurrence due to our radar coverage. I told him radar contact lost and to expect identification soon. He didn't respond. I tried him on my other transmitter. I didn't get anything back. It is also fairly common to not be able to hear aircraft at that altitude in the area. I didn't think much of it. Then a few minutes later; I was shipping an airplane who told me they were hearing an [Military] aircraft on guard who said they couldn't maintain altitude and needed vectors to the closest airport. I asked the pilot if the call sign was [Aircraft] and they said it was. I told the aircraft to remain on my frequency and immediately began to try and relay through them. I relayed that I had lost [Aircraft] on radar and said where the nearest airport was reference their last position before I lost radar.I kept trying to relay through various aircraft; assuming [Aircraft] was in an extreme urgency situation. A few minutes later I saw [Aircraft] come back up on my radar below the MIA in the area. I relayed to an airplane where another nearby airport was. I had an airplane relay to me that the aircraft wanted vectors toward their destination. In lieu of radar-identifying the aircraft through a relay and given the situation I made the judgment to believe that the radar hit correlated with the aircraft in question. I relayed to have them fly a heading toward their destination as requested. At this point; it appeared they began to climb again. I relayed to have them maintain an altitude at the MIA; which they were back at. I then tried to talk directly to the aircraft. This worked momentarily; but then I couldn't get them to read anything back. I relayed through another plane that they were radar contact again and to maintain their current heading and altitude. I then relayed a frequency change to Approach. I did not ever ask why they couldn't maintain altitude; nor did I try to relay a safety alert. I believed the pilots were in a very; very stressful situation and knew that they were in an unsafe situation. Resultantly; my goal was to give them whatever assistance I could to get them pointed toward their airport of choice.

Data retrieved from NASA's ASRS site 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	1701504
Time
Date	201911
Local Time Of Day	1201-1800
Place
Locale Reference	ZSE.ARTCC
State Reference	WA
Aircraft 1
Make Model Name	S-70/UH-60 Blackhawk/Seahawk/Pavehawk/Knighthawk
Flight Phase	Cruise
Route In Use	Airway V204
Flight Plan	IFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 2.0
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT

Center controller reported a helicopter in an area of no radar coverage and intermittent radio coverage experienced difficulty and descended below the minimum IFR altitude.