A well-known operating condition of Airbus aircraft may have played a role in the TCAS resolution that kept two airliners from getting any closer together in a Dec. 18 incident at George Bush Intercontinental Airport in Houston. The Volaris Airlines A320neo and a United Express E145 operated by CommuteAir came within about 750 feet of each other as they climbed from parallel runways 33L and 33R. The Airbus crew was told to make a teardrop turn left to a heading of 110 and the pilot read it back correctly. But instead of turning left, the A320 turned right and converged on the Embraer. Both crews got a resolution advisory from their TCAS systems and got out of each other’s way before heading off safely for their destinations. Airline pilot forums lit up with what seems like a reasonable explanation for the wrong turn.
The turn ordered by ATC for the Airbus required a 220 degree turn to the left. Pilots on the forums explained that when the heading is set on the A320, it will take the shortest route to that heading, in this case the 140 degrees to the right. A pilot on the Airbus read back the initial clearance correctly and when the plane turned to the right, a pilot, perhaps not the same one, asked for confirmation of a right turn to 110. The controller corrected him and said it was a left turn. Shortly after that, the CommuteAir crew reported the RA and was given a sharp right turn to get away from the Airbus, which continued its teardrop turn to the left.
That was a tough one to watch knowing what was coming. I thought the controller did a good job pre-departure with the way she repeated “left turn” in the instructions. I think she stumbled with the incorrct “yes” when things started to unravel.
I would like to hear the rest of the story on this one….
I sheepishly admit to making this mistake of not knowing my right from left on the fly and not realizing the controller wanted me to make a turn that took me “the long way around”. I have tried to develop the habit of looking at the L and R on my turn and bank indicator when reading back instructions containing the words left or right.
I also recall something from a ground school class more than 15 years ago about parallel ops where the airplane not making the mistake is the one that should break off…. I recall it being an approach/arrival thing and maybe unique to Dallas?
A very minor contributing factor might be that English did not seem to be the first language in the offending aircraft. This is inexcusable, but a possibility.
I realize it is non-standard phraseology and unlikely at a major hub with constant parallel ops, but I might suggest something like, “….left turn, the long way around, to 110…” or “….for deconfliction due to parallel operations, left turn to 110…”
Although seldom needed, but as a controller I always said, “turn left, the long way around to heading….
An error induced by aircraft flying itself instead of pilot flying the aircraft?
When the AP is in HDG mode and you spin the heading bug more than 180 degrees in one direction — left in this case, every system I’ve ever operated from transport category airplanes to my RV-7 will turn in the directions of “lesser degrees”. The PM did that to me once on a night takeoff in the Saab 340 and the flight director suddenly switching directions was very disorienting. Pay attention when you spin that bug around!
Every airplane I’ve ever flown does exactly that. My guess is they just heard 140 and their confirmation bias told them to turn right.
Every HSI I’ve ever flown with, mechanical analog or electronic, turned to a new heading via the shortest angle. I learned 40 years ago never to slew the heading bug more than about 170° in the direction I needed to turn, then slew it the rest of the way when I was within 170° of the final heading, and I’d wager 99+% of pilots flying with autopilots in the heading mode know that. So, I’m wondering, in modern airliners, does selecting the new heading also involve selecting the direction of turn? (I have no experience with the big iron.)
A lot of things we learned 40 tears ago are no longer true. The 179º heading change limit is one of them unless your autopilot is 40 years old. Every autopilot I’ve flown for the past 30 years or more will continue the turn in the direction the heading bug was slewed up to 359º. If you select a heading prior to engaging heading mode, they will turn the shortest way.