This is something we hear frequently enough, perhaps once every three or four flights when an airplane in close proximity is climbing rapidly with a clearance to level off 1,000 feet below us. The TCAS (Traffic Collision and Avoidance System) is just giving us a warning that, should the airplane not level off, we may have to take action.
We were at FL390 (39,000 feet), an altitude where the traffic warning was far less likely. The captain and I looked down at the TCAS screen to get a quick idea where we should be looking for the other airplane. It was 800 feet lower than us and at our 2 o’clock position. It was easy to spot, with huge puffy contrails billowing out and slightly below it. A 737 for sure. We were both satisfied that it would pass behind us, since it was moving from left to right across the windscreen. A stationary position in the sky would mean it was coming right at us.
But before we could discuss this passing airplane, the computer voice came on once again.
“Climb, Climb now!”
Our procedures dictate that we should honor thy TCAS request, known as a Resolution Advisory or RA, by disconnecting the autopilot and following the rate of climb commands computed by the TCAS system.
Since it was my leg, I immediately disconnected the autopilot, while glancing down at the vertical speed indicator to find out just how many feet per minute of a climb would be needed. It wasn’t much, in fact. Just 200 feet per minute, hardly even noticeable to the passengers. It commanded a level off when we were at 39,100 feet and shortly after allowed us to settle back down to our original altitude.
All this was done in a matter of seconds, with no input or guidance from Air Traffic Control. In fifteen years using TCAS, this was only my second resolution advisory-the other one having occurred while on approach just east of Port-Au-Prince Haiti years ago.
“Center, confirm we were cleared from 380 to 400?” The other aircraft asked.
The controller said yes, which made us think this could have been an error on the part of the controller.
“Can you explain then what just happened?” The 737 pilot queried.
We let the controller know that we had also just responded to a resolution advisory. The other pilot asked for a phone number of the Air Traffic Control center that he could call. We copied this number down as well.
There was some discussion between the captain and I whether we needed to report this as a near midair collision (NMAC). I pulled my manuals out, now conveniently located on an EFB equipped iPad (Electronic Flight Bag) and searched for the NTSB criteria for a near midair collision. Nothing came up.
But I did find an interesting recent change to our procedures. The NTSB (National Transportation Safety Board) requires that any flight responding to a TCAS resolution advisory above 18,000 feet must pull the voice recorder circuit breaker after completing the parking checklist. This would allow the NTSB to analyze the tapes from ATC and the aircraft involved in the loss of separation incident.
Just knowing that the NTSB would be listening to our conversation for the next two hours tends to make you aware of every word you’re saying. In fact, I debated with myself about getting into a discussion during our approach briefing about wind and gust additives that we would be applying for the approach.
I recognize that there’s value in allowing the NTSB access to the conversations that led up to an incident. They’ll hopefully study the procedures and policies that could prevent this kind of situation. There’s still a big brother feel to it.
I couldn’t help but feel bad for the controller on duty. While the captain and I were waiting for the employee bus, he phoned the air traffic control center. The controller explained that a clearance was given to the Trans-Siberiana 1701, but that Trans-Siberiana 1790, who had also asked for a climb, had accepted the clearance instead. All airline names have been changed to protect the innocent.
I looked up the FAA definition of a Near Midair Collision:
A near midair collision is defined as an incident associated with the operation of an aircraft in which a possibility of collision occurs as a result of proximity of less than 500 feet to another aircraft, or a report is received from a pilot or a flight crew member stating that a collision hazard existed between two or more aircraft.
It turned out we were just a 100 to 200 feet away from the NMAC definition. So I guess it was “nearly a near midair collision.”
We both filed a report detailing the events. I recently received the response. We did everything by the book and it obviously wasn’t our fault, which meant that the case was closed as far as our involvement.
Someday I hope we’ll have a third layer of safety in addition to the protection offered by ATC and TCAS in the form of a two-lane airway using a half mile offset to the right. Ever since GPS was invented, we have reduced the normally 8-mile wide airways down to just a few feet thanks to the precise nature of the technology. But with that came greater reliance on TCAS to keep us out of trouble. I wrote about an inexpensive offset airway proposal previously and I’d love for the FAA to take another look at it. Adding layers to our safety net is what has made air travel so much more safe than in the early years of flying.
Cockpit Chronicles takes you along on some of Kent’s trips as an international co-pilot on the Boeing 757 and 767 based in Boston. Have any questions for Kent? Check out Plane Answers or follow him on Twitter @veryjr.