Calling Tower
Wake Turbulence
Take-off Clearance
Clearing the Zone

Calling Tower

When he is sure his checklist is complete and he's ready to go, the pilot tunes up 120.8, Moncton Tower's frequency, and like a good pilot, listens for a moment to ensure he doesn't interrupt a radio exchange already in progress. Continuing to show good radio etiquette, our pilot formulates his transmission, and then, when other radio traffic permits, hits the PTT button to make his call:

CGOOF: "Moncton Tower, Cessna Golf Oscar Oscar Foxtrot, holding short of runway two niner on Alpha, ready to go."
CYQM_TWR: "Cessna Golf Oscar Oscar Foxtrot, Moncton Tower, taxi to position runway two niner and wait. You're number two for departure after a seven fifty seven off runway two four."
CGOOF: "Oscar Oscar Foxtrot."

Many pilots would respond to such an instruction a little differently than posted here. I think it would make a reasonable statistic to say that most would say something to the effect of, "To position and wait, Oscar Oscar Foxtrot." In either case, "taxi to position" means that the aircraft is allowed to proceed onto the active runway and line up for departure, but not allowed to do anything else, including anticipating take-off clearance by starting to roll. Please note that this doesn't mean the aircraft is allowed to backtrack on the runway (some refer to this as "back taxi", which means to taxi in the direction opposite to that used for take-off -- in our case, backtracking runway 29 would be the same as taxiing on runway 11, if you can picture that). If the taxiway doesn't reach the end of the runway, which is often the case, and the full runway length is required, which is also often the case, the pilot must receive a clearance which specifically authorizes the backtrack operation. Having said that, ATC would never expect a B747 to taxi out and do an intersection departure on an 8,000 foot runway when the taxiway he is in is 4,000 feet from the runway threshold. Many have debated the requirement, or lack thereof, for ATC to specifically state the backtrack instruction in such a case, or for the pilot to specifically ask for it if it were not forthcoming without asking. Airmanship comes into play here, I think, and ATC shouldn't issue such a clearance without the backtrack instruction in the first place, in my opinion. By the way, ATC MANOPS 336.6 is the paragraph that tells ATC they must provide a sequence and traffic information to OOF here, since he is not number one to go.

Since a take-off clearance wasn't the transmission from ATC, they included the reason for the delay, which is a requirement on their part according to ATC MANOPS 336.1. This helps reinforce the fact that the aircraft isn't cleared to go. In the past, the phrase, "Taxi to position and hold," was given, and the pilot said he heard, "taxi to position and roll". Quite a difference, since he actually thought it was an informal phraseology meaning, "cleared for take-off". Sometimes it's easy to see why ATC has standard phraseology, and why they should be sticking to it. In the case of such an instruction, there is no requirement to readback the traffic information. The most I'd suggest, if you really want to read something back, is to just read back the instruction to, "taxi to position and wait." Oddly enough, I noticed while researching this topic that the example in the AIP RAC 4.1.1 actually has the tower using the phrase, "taxi to position and hold..." I wonder who wrote that part...

A little bit of airmanship comes into play, now. Before entering any runway, whether at a controlled airport or not, a pilot should act like a child looking both ways when he crosses the street. The "walk" light being on doesn't mean there isn't a car coming. You wouldn't cross without looking, would you? You shouldn't enter a runway without looking, either. Runway incursions are a very high profile item worldwide, so vigilance is high in the minds of ATC, but just the same, it takes so little effort to have a look out the window and scan the sky when weather conditions permit.

Wake Turbulence

So our pilot enters the runway, after looking and ensuring it's clear, and lines up on the runway numbers. Looking down the runway centerline knowing I'm about to hit the blue is always an exhilarating point in any flight for me. Now the pilot searches the runway ahead for any signs of vehicles, animals or whatever else might pose a threat to a take-off roll, while looking for the 757 traffic tower mentioned. Then the radio crackles to life again:

CYQM_TWR: "Fast Air one two three, winds two eight zero at five, contact departure one two four four airborne, cleared take-off runway two four."
FastAir123: "One two four four in the air, cleared take-off two four, Fast Air one two three."
CYQM_TWR: "Oscar Oscar Foxtrot, the seven fifty seven is just rolling on two four now. There'll be a three minute delay due wake turbulence."
CGOOF: "Oscar Oscar Foxtrot."

Notes. More notes. First off, check out the format of the take-off clearance issued to the B757. For the ATC types, the format is important. In the past, aircraft in receipt of a clearance worded, "FastAir123 cleared for take-off, winds 280@5, contact departure on 124.4 when airborne," have missed completely everything after the words "cleared for take-off" were said. Impatience, urgency, "get-home-itis", whatever, often would have pilots throttling up and saying, "yeah, yeah, here we go." ATC is now required to say everything needed first, and the words, "cleared take-off runway 29," last. This has proven that more pilots hear and understand the other stuff, too.

MANOPS permits ATC to provide a take-off clearance without the wind speed and direction if the winds are less than 15 knots (M336.11). Winds in excess of 15 knots are to be said before the take-off clearance. As an airport controller, I would often include the winds, especially if they were a noteworthy crosswind or tailwind, since the aircraft would often ask if I didn't include them. As a result, I opted to give them almost every time, unless they were less than 15 knots and timing seemed ultra-critical. My experience as a pilot leads me to believe this is a common practice outside where I once worked as an airport controller, but it may very well not be. As a pilot, I like the hear the numbers.

Now, if both aircraft were light category aircraft, ATC could clear OOF for take-off on 29 as soon as the aircraft departing 24 crossed 29. MANOPS 336.16 now sheds light onto why the Tower would provide the next transmission to OOF. It tells the airport controller to provide the reason for the delay of the take-off clearance and the position and type of aircraft if the take-off clearance is being delayed solely due to wake turbulence and a pilot initiated waiver can be granted. The idea is to provide the pilot with the option of waiving ATC's requirement for the provision of wake turbulence separation. To promote safety, ATC will provide light aircraft with additional separation when operating behind medium or heavy aircraft, and all aircraft (including heavies) operating behind heavy aircraft in many situations. In our situation, the pilot is flying a light aircraft (C172) intending to take-off from a runway which crosses the runway used for take-off by a heavy category aircraft (B757 is treated as a heavy for wake turbulence purposes). The separation required according to MANOPS is three minutes. In this situation, it is possible for the pilot to ask ATC to waive this separation, which means the pilot is now asking for sole responsibility for avoiding the wake turbulence. A future topic may be done on this issue, since it is pretty important. Note, also, that despite the additional separation ATC provides, controllers are in no way guaranteeing that the dangers of wake turbulence are over after the delay. The pilot is always in the best position to determine the level of risk when considering wake turbulence, and the pilot may deny a take-off clearance for a longer period if he chooses. This may mean that ATC has to get him off the runway for other traffic, should he choose to wait longer, but that's the pilot's call.

Take-off Clearance

Our pilot examines the situation as he watches the B757 roll. Runway 24 is only 6,150 feet long, and the pilot used a good portion of that before he even rotated, let alone got airborne. With about 7,500 feet of runway between where he is sitting and where the intersection of the other runway is, our pilot knows he will rotate and climb well above the flight path of the B757. Since the wind is only 5 knots on the surface, he can get well above that before the wing tip vortices will bother his take-off, if he goes soon. Since he is ready, he decides to ask for a waiver to the wake turbulence separation.

CGOOF: "Tower, Oscar Oscar Foxtrot request a waiver for the wake turbulence. I'm ready immediate."
CYQM_TWR: "Oscar Oscar Foxtrot, caution possible wake turbulence from the seven five seven that departed runway two four. Winds two eight zero at five, cleared take-off runway two niner."
CGOOF: "Oscar Oscar Foxtrot."

The take-off time is recorded, and the throttle eased smoothly forward. The standard circuit pattern is left hand and there was nothing to the contrary regarding circuit direction for runway 29 at CYQM in the Canada Flight Supplement. This means the pilot doesn't need to ask for a left turn out. The plane as loaded climbs quite well, and the pilot decides to initiate a left turn well prior to crossing runway 24. This keeps him out of the path of the B757, and away from the wake turbulence. As soon as he is at a satisfactory altitude, the left turn is made.

Clearing the Zone

Eventually, the aircraft clears the control zone to the south. In this case, Moncton's CZ is 7NM, and 3,500 ASL. He's climbing well, but not that well, so he ends up leaving the zone laterally, rather than breaking the cap. A report is made at an opportune moment when the radio is otherwise quiet, and it goes something like this:

CGOOF: "Tower, Oscar Oscar Foxtrot clear of the zone to the south, out of three thousand two hundred for three thousand five hundred."
CYQM_TWR: "Oscar Oscar Foxtrot, roger. Radar services terminated, you're cleared enroute frequencies."
CGOOF: "Oscar Oscar Foxtrot."

It is a good idea to monitor the tower's frequency for at least a short time after leaving, just in case an inbound aircraft calls up entering the zone from your general area. OOF monitors tower until about 10 or 12 miles south and is satisfied he won't interfere with anyone else. A good "enroute frequency" for this point of flight depends on what the pilot intends to do. If he wants flight following from the local IFR unit, he can change the same frequency assigned to the B757 that departed ahead of him, 124.4. If he wants to go on his own, then he should, in the absence of other frequencies assigned on charts, monitor 126.7. This way, someone can get a hold of him if required.

Well that was painless. Any comments or questions? I'd love to hear them. Send anything to me through e-mail (leave the viruses at home, please) to moxner@nbnet.nb.ca. Thanks for taking the time to read!