Slot City

I'm on the 4th of 6 early starts. Each day I'm awoken from a deeper sleep by the alarm clock at o'dark hundred and each day the disappointment gets greater and greater as I realise I am actually working, rather than forgetting to turn the alarm clock off or it being a bad dream.

It's a case of dejá vu each morning, the quiet roads on the way to work, the same aircraft sitting awaiting departure each morning, and equally unfortunate bleary eyed crews turning up and exchanging sympathies about how many earlies we're doing. Greeting most pilots in the morning, after the usual mutual moaning of fatigue the next question is always 'Is there any slot?'

Early morning is a busy time for both airports and the airspace around them. With a wave of departures all wanting to leave at the same time and follow the same pieces of airspace to the same destination, or destinations close by, their flow has to be regulated. That's where the black art of slots come into play in Europe.

I don't work in flight planning ops or air traffic, so the following simplified explanation will probably leave some banging their head and comparing me to an uninformed journalist trying to report on some minor aviation incident, but alas, I'll have a go.

Each flightplan filed in Europe goes through a computer known as CFMU, or Central Flow Management Unit. I imagine it as a massive super computer stored in a darkened room with it's own micro-climate, with many operatives nurturing it and keeping it happy. In return, it will crunch many numbers and try and attain the most efficient use of airspace around Europe, keeping things moving and preventing bottlenecks at busy spots. To attain this regulated flow, it devises a time for each aircraft to depart/arrive/pass overhead a point, and this results in a Calculated Take Off Time, or CTOT. Since modern flight planning is so precise, sectors of many hours can usually be accurate to a minute or so easily, it churns out a CTOT for a flight so that it should progress smoothly.

This CTOT, or slot as it's commonly referred to, is the time the aircraft should be taking off at. This puts added pressure on everyone, if the slot is missed it could be a long time before the flight gets another one. Although the CTOT is an actual time, there is a discretion of -5 to +10 minutes that provides a window that the aircraft can depart in. However, it's to be used only by the local Air traffic controllers, to allow them to work the aircraft into the flow of traffic on the ground, since it won't always be possible to have it at the runway at that exact time. For us the ground crew, we're working to get the aircraft off stand 10, 15 or 20 minutes before the CTOT, depending on the ramp traffic and taxi time.

So on any early morning, it's not unsual to have most of the departures having slots. This messes up the usual order of departures we would be expecting, as a flight due to depart at 0630 may have a slot of 0720, but a flight due to depart at 0635 may have a slot of 0642. It's also not unsual to have a slot that results in the aircraft having to depart the gate early in order to make it. Slots often tend to change as well, as the traffic flow changes. In the space of the hour leading up to departure, it can be common to have the slot to change three or four times, jumping forward or even backwards.


Finally getting around to taking a picture now and again, without giving too much away about where I work. Below is one I took recently, the panel located on the back of the nose gear strut of a 767. You can see some of the buttons I talked about in a post last year when discussing the headset conversation. Don't be tempted to push the large red or black button...unless you really need to! You'll just create endless amounts of paperwork for yourself, and a no tea and biscuits meeting with the manager.



The headset lead plugs into the jack on the bottom left, titled Flight Interphone. The wheel well light switch controls a light inside the wheel well so it can be easily inspected, and the switches relate to the APU, so that it can be shut down and the fire bottle discharged should anything happen.

2 earlies to go...then some proper sleep!

The secret conversation

I apologise for the silence over the past two weeks but I've been kept busy, not with work, but other things. Hopefully I'll get a bit more writing accomplished over the next few weeks. Continuing on from my last post about walk around checks, this one will give you a little insight into what the guy wearing the bright luminous headset is doing during push backs.

So with my walk around checks complete I'll plug-in the headset so I can communicate with the crew. If it's familiar type like the A320 or 737s, I know where to find the plug. If it's something I'm not used to working with such as an ATR, I'll stumble about around the nose and gear looking for some sort of plug to connect the headset to because I forgot to ask the crew where it is when talking to them.

Once I'm plugged in, depending on the aircraft, I'll either give the Push to Talk (PTT) switch on the headset a click to let the crew know I am now ready when they are, or stand in their line of sight awaiting their call. For 737s, I can easily stand within the headset cable's extension and the first office or captains line of sight, as they sit much lower than the A320s. For the Airbii, I'll give a a quick mike click, as to see the flight crew I would need to move a considerable distance out from the aircraft stretching my precious cable. It extends to something like 12m when stretched but I never pull it this far as I don't fancy trying to recoil and carry 12m of cable away once finished.

Some aircraft have a Pilot or Flight deck call switch located next to the port for my headset, though I've never used it it. I figure the last thing they want is another ding or dong going off in the cockpit as they make the final preparation before push back.

Speaking of thee Pilot call buttons, I was almost caught out once with a 767. On the 767s I have worked with, the headset plug is located on the back of the nose gear together with some other buttons. Beside the headset plug is a LARGE RED button, and most, including myself would assume it is the flight deck call switch. Assume nothing. Experience has taught me flight deck call switches are located next to the headset plug, but equally experience has taught me not to push large red buttons unless I'm certain I know what they do. The red button is in fact an APU fire extinguish button. Press it and I'm sure you will get the attention of the flight deck, but more a long the lines of chronic swearing as they wonder why the APU has just died and the fire bottle discharged.

When the crew are ready, the First Office or Captain will speak to me on the headset, depending on company procedure, generally starting with,

"Cockpit/flight deck to ground, helloooo?''

I'll respond with a hello with more o's than his. Again, dependent on the airline procedure or the captain in question, he may well ask for my checks to which I reply that all the aircraft doors and hatches are secure, ramp workers and equipment is out of the way, the chox are removed from the wheels, and the steering by-pass pin and tug are all in place.

By this stage, he may already have his clearance from Air Traffic Control or ramp control, to push back. If so, he'll tell me they're cleared for push and start, together with which runway they'll be departing from. It's important I know which runway or taxiway he'll be taking after the push back, so as I leave him pointing in the right direction. So providing both parties are ready and clearance is received, I'll ask him to release the parking brake and wait until he replies with a unambiguous 'Parking brake released, cleared to push' message or words to that effect.

Ground to Flight deck?
Go Ahead
We're ready for push back, release parking brake please.
Parking brake released, cleared to push for runway 30/taxiway Golf etc.. let us know when we can start engines
Ok pushing back, standby for start.

The aircraft is now 'in my control' through the tug. I signal to the tug driver the parking is off and we can push back, and through a series of further embarrassing hand gestures making me look like an 1980's dancer, tell him what direction to leave the aircraft facing.

So as we start moving back, I'll be on one side of the aircraft watching the wingtip making sure we don't hit anything, and a colleague will be on the other side doing the same. When it's safe to do so, I'll inform the flight deck they are clear to start engines and they'll let me know the sequence they are starting, such as no.2 first followed by no.1

Clear to start number 2 and 1 as you wish
Starting engine 2 then 1

As the engines start up, I'll observe them to make sure nothing out of the ordinary happens such as black smoke, or foreign objects being sucked into engine or fire. I believe there are still some airlines who require the person on the headset to be an engineer for the push back, but none that I deal with.

When we have finished pushing the aircraft and come to a stop, the tug driver will signal to me that he has set the brakes. I'll call the flight deck and ask them to set the aircraft parking brake again. Once I'm told it's set, we'll start disconnecting the tug, towbar and remove the pin from the nose gear. If all the engines have been started and everything appears normal by this stage, the crew will inform me I can disconnect, revert to hand signals and show them the pin.

I'll reply and tell them what side to look for us on for the hand signals, wish them well and disconnect myself from the aircraft. I'll then walk with my colleague to one side of the aircraft, my friend will hold up the steering pin he has removed, that has a large red flag attached. It tells the crew they now have steering control back, and I'll give a thumbs up signal followed by a wave letting them know we're all clear from the aircraft.

Ground to flight?
Go ahead...
Push complete, set parking brake please
Parking brake set, 2 good starts, clear to disconnect and revert to hand signals, thank you
Ok watch for the pin on the left, good morning


I told you it wasn't exciting, but maybe the next time you're sitting at the gate and your companion asks what the guy on the headset is doing you'll be able tell them. However that's just in my part of the world and how we work, I'd be interested in what it's like elsewhere. Any input from crews on their experiences with ground crew and push procedures would be interesting.