TCAS Resolution Advisory in IMC
- Tony Wallace
We were in Morristown, NJ (MMU) for a trip to Bedford, MA (BED). It was a relatively short flight and our last leg of the day. We would be at the hotel before dark and would be the end of a great day of flying.
The weather at Morristown was 500 broken, 1000 overcast with 3 miles visibility in light rain and mist. The weather at Bedford was clear.
We departed from MMU and checked on with New York Approach. We were vectored on course and cleared to 3000 feet. Level at 3000, we were still in IMC conditions. We were given climb clearance to 4000, and as soon as we started our climb, our TCAS Gave us a Traffic Alert (TA) for an aircraft a few hundred feet above us.
When reported to ATC, the controller said, "Yeah. He is VFR at 4500 and I am not talking to him." We agreed to remain level until clearing this traffic. About two seconds later, TCAS gave us a Resolution Advisory (RA) that said "Descend!!! Descend Now!!!" I immediately complied with the RA.
While descending, the TCAS strengthened the RA to "Increase Descent!!! Increase Descent!!!" This was followed very shortly by the EGPWS warning of "Caution Terrain, Caution Terrain" then followed by "Clear of Conflict." When we received the "Clear of Conflict" annunciation, there was 200 feet separation and less than a mile.
All of this took place faster than you were able to read the paragraph. While the event was occurring, my PM was looking for traffic and in continuous communication with ATC. At one point the controller stated, "I have no idea what he is doing, but he is tagged and we will track him to his destination." It turned out to be a V-tail Bonanza who was trying to descend through a "Sucker Hole." Without TCAS, I probably would not be writing this.
This scenario brings up some good points associated with TCAS.
- TCAS does not consider IFR/VFR status or pilot intentions.
- Don’t deviate from an ATC clearance solely based on TA information.
- Promptly follow RA guidance and inform ATC if deviating from a clearance.
- Return to your ATC clearance after receiving the "Clear of Conflict" call.