Driving to work today first thing I noticed was an empty apron. The aerodrome I work at happens to be home of the training academy for our military. They fly CT4's, not exactly sure how many they have but it must be close to twenty. The two in the picture are actual aircraft from the academy. We refer to the apron being empty as "bases loaded". Its a common scenario, I had a late start (11am), the early start had spent the morning processing a whole bunch of departures and I was just in time for all the arrivals and circuit training.
ADC2 isn't really all that difficult. It has its moments of frustration but a large majority of the time it easy going. Its the ADC1 controllers who get the headaches. Today was pretty straight forward. I think the most I had in the circuit was six aircraft with just a few arrivals in between and only a couple of departures at the time.
Six in the circuit is a good number. There's still plenty of room and not too much congestion on the radio. I think I only had a two or three aircraft over transmit today. Every over transmit puts you a few seconds behind, with six in the circuit its easy to recover but when you have eight or nine it gets a bit ridiculous. But there are ways to handle the traffic intensity. Holding any departures on the ground for a couple of minutes is always a good one. Probably frustrating for the pilots on the odd occasion but its safe. And at the end of the day that's what its all about. If safety wasn't a concern then I wouldn't have a job and pilots would separate themselves. I didn't have this drama today. It was pretty straight forward and I went home.
What I might do is bring up something that happened a few months back. As an Air Traffic Control you must apply various "separation standards" on a daily basis. They come in all shapes and colours, one group of them being runway standards. I can't speak for everyone but I have pretty much figured out some of the pilots I deal with don't have an understanding of runway separation.
The standard I was applying this day was one relating to a landing aircraft behind another landing aircraft. This is only one of about five or six but this one allows the controller to clear an aircraft to land while the runway is still occupied by the preceding landing aircraft. I'd like to make a note to my international visitors that separation standards vary in different countries.
This standard states:
A landing aircraft shall not be permitted to cross the landing threshold unless, in the opinion of the tower controller n, no collision risk exists, and:
- the landing aircraft has a MTOW below 3,000kg and is a performance category A aircraft; and
- the preceding aircraft has a MTOW of 7,000kg or less; and
- if landing will vacate the runway without backtracking...
I was reasonably busy this day. I had multiple other traffic on frequency but as for the two aircraft in question, one was cleared to land and yet to vacate the runway and one was short final. Both were CT4's so section 1 and 2 of the above standards requirements were met, the preceding CT4 did not have a clearance to backtrack and it wouldn't be required so section 3 was covered and my opinion was that there was no collision risk. The CT4 on final was cleared to land.
During my training and still to this day on my checks (we are required to do routine performance checks) I have had it drilled into me to ensure I do "my runway scans". With every clearance on the runway we are required to scan the runway to ensure it is cleared. Twice. Once with the clearance and once just prior to the aircraft using the runway. In this case my first scan was with the clearance noting the runway was still occupied but there was no collision risk. With my second scan I noticed the preceding CT4 on the runway had missed the second exit and had decided to help himself to a short backtrack. At this instant I no longer had the above standard and the aircraft on final, by this stage close to the runway threshold was sent around. Would the two have collided? Probably not, but there was definitely a possibility.
In text this sounds like a problem with a simple solution. In reality the controllers attention is shared amongst a dozen aircraft and a situation that occurs in a matter of seconds is easily missed.
So how could this situation be avoided in the future? Firstly I'd like to say that an aircraft requires a clearance from ATC to backtrack a runway, everyone knows that. A better appreciation for what the controller is trying to achieve could also help the situation.
That's the job though and that's why we are there.