Parallelism: the quality or state of extending in the same direction, everywhere equidistant, and not meeting.
Hello dear reader,
I hope you are doing fine and staying healthy.
I chose to tell you this story today because it should remind us all, pilots and controllers, that nobody is sheltered from mistakes, even in interpretation or errors judgement. When I started training to become a controller, one of the first things we were told by the director of operations was: “If something can go wrong, you can be sure that, at some point, it will go wrong”.
Although we were still before people talked about the “Swiss cheese model”, it sounded like a very valuable piece of advice, even to untrained ears.
The situation takes place on a medium-sized international airport with two parallel runways. The most usual runway configuration is that the left runway is used for arrivals, and the right for departures and a few excess arrivals if need be. As a matter of fact, the left runway doesn’t even have taxiways to the threshold as it is so rarely used for departures. But then, sometimes it does happen once in a while that a pilot requests to depart from the left runway when too heavy, because of the position of obstacles in the departure path of the right runway.
And it is on one of those occasions that the following situation happened.
On the left runway, we have a long-haul heavy aircraft backtracking before departure, and on the right one is a medium haul jet lined up. The departure from the left runway has a right turn out after departure, and, as fate would have it, the one from the right runway has a left turn out when passing 1700 feet.
It looks dangerous, or complicated, but as a matter of fact, the solution is very simple for the controller. Let one depart, and once it crossed the extended axis of the other runway, the second can go freely.
So, since the traffic on the right runway is ready to go first, has less wake turbulence and is expected to have a better rate of climb, the controller clears them for take-off first. But the first problem appears.
ACFT:” Erm, tower, we are not able to depart right now, we just discovered we are missing our catering. Request to return to the gate”
TWR:” Roger MED123*, vacate the runway first left and contact ground 121.8”
Easy. No big deal, and it solves the separation with the parallel departure, doesn’t it? So, the controller turns to the other traffic, on the left runway, which is in the middle of its 180-degree turn to line up.
TWR:” BIG456*, cleared for take-off runway 27L, wind 300 degrees, 7 knots”
ACFT:” BIG 456, cleared for take-off”
And since it is a rare sight, the controller looks at the airliner hurling down the runway, to make sure all is ok. Then, almost mechanically, the controller goes back to the right runway to see who is next in line for departure and to see if the traffic has vacated. And his heart skips a beat or two.
The traffic which was supposed to vacate the right runway is rolling at full speed, is already nose up and will clearly not vacate the runway and go back to the gate. What happened in the aircraft is that the crew in fact found what they were looking for, and elected to go anyway.
Quick pause: we have two aircraft taking off from simultaneously from parallel runway, and are bound to turn towards each other in a matter of seconds. Not good.
Fortunately, as the controller called immediately his colleague doing the radar rector handling departures, one of the pilots had already switched frequency and was listening to the departure frequency, so appropriate instructions could be issued. The proximity was still bad, the near miss was a very serious one, but fortunately, no accident happened.
Remember? “If something can go wrong, you can be sure that, at some point, it will go wrong”
Many fingers are already pointing at the pilot of the jet that departed without clearance, right? Well, let’s think again. Of course, the pilot had received the instruction to vacate the runway, but it is a bit more complicated than that. Once a take-off clearance has been issued, if, for any reason, it becomes invalid, it MUST be cancelled before anything else. This is the perfect example of a situation where too many things were left “unaddressed”. The controller should have cancelled the take-off clearance to make sure that everything was “locked”, and nothing could go wrong.
I have personally seen many other examples, but none as graphic as this one.
Dear friends, whether you are a pilot or a controller, I cannot insist enough: If you ever are in a situation where something is unclear, or may leave room for interpretation, I am urging you to clear everything up. Dot every “i” and cross every “t”. And here it is once again: “If something can go wrong, you can be sure that, at some point, it will go wrong”. Courtesy of my former Director of Operations.
Have a nice week, and stay safe my friends.