On Saturday morning, Lisa came into the living room as a train went west from Fernley and told me that there were eight locomotives on the head end. Must be an equipment-equalization move, I speculated, as Lisa headed off to do other things. I then heard over the radio the crew of that train tell the dispatcher and tell him that they'd had an unplanned emergency brake application.
Trains are big and heavy, so while an emergency brake application halts the train, it doesn't stop it immediately. By the time the train had come to a stop, the rear of the train was opposite our house (but the view was obstructed by two tracks in Fernley's small yard with cars spotted in them) and the head end was fouling the switch at West Fernley. That means the Nevada Subdivision was plugged until the cause of the problem could be found and corrected.
Fortunately for all concerned, a UP local freight was in the area following this train on their way back to Sparks Yard. The dispatcher instructed them to come up alongside the stalled train, drop a crew member to inspect the train starting from the rear while the conductor of the mainline train started walking from the head end.
Lisa and I could both hear the sound of a lot of air blowing from the train. She suggested that, since the end of the train was right in front of our house, what we were hearing was an air hose that had come off the FRED.
Lisa brought her camera as we ventured out to (safely) see what we could see. She shot four short videos that take in the sequence of events. These were not easy to shoot, as they are using a telephoto lens at a high magnification without a tripod, while shooting through the gaps in a center-barrier car on the near "house track" and a tank car on the far track.
The hose hanging loose is the air line in question. You can hear the air hissing from the line, which should be attached to the FRED (not quite visible on the coupler above the loose hose).
The local train came up, dropped a crew member, and then continued on up toward the head end of the main line train.
The local's crew member confirmed that air was coming out of the loose hose and prepared to fix it while his train rolled west to work with the crew of the mainline train.
The local's crew member turned the valve that shut off the air (you can hear this plainly), reconnected it to the FRED, then turned the air back on. You can hear the FRED come back to life.

With the problem fixed at the rear end, he started walking on the south side (the side that faces our house) toward the front of the train. We'd heard on the radio that the conductor of the mainline train was walking the north side. Both crew members would be inspecting the train for any other loose hoses or other damage. You can see me at left, holding the camera bag and walking back toward the house. The UP crew took no notice of either Lisa or I.
While this was going on, the dispatcher was facing the problem of a "Z" train (high priority intermodal, such as UPS and FedEx packages) heading this way and no way for them to get through, with the mainline train blocking the main, the siding plugged with the local, and a "dead" mainline crew. The two sets of crews and the dispatcher put their heads together and worked out a solution.
2. The local crew would take charge of the mainline train and back it up so that it no longer blocked the switch, but was instead between switches on the main line in Fernley.
3. After clearing the switches, the local crew would tie down the mainline train — "parking" it there. A "dogcatch" crew would be dispatched later from Sparks to collect the train and bring it to Sparks.
4. The local crew would then take their local on in to Sparks as originally planned. As soon as they moved up to Thisbe siding (or farther, depending on how far the Z train had progressed), the line would be open again and the Z would be able to get through. It's not ideal to have to put a high-priority Z train through the slow siding switches at Fernley, but it's better than not having it move at all.
Lisa and I went for a drive shortly after recording this mini-drama. Around the time we got back home, the "dogcatch" crew had arrived and were easing the train out of Fernley to take it to Sparks.
Other than being an annoyance, there was no danger here, especially after the crews identified the source of the emergency brake application.