Aviation Topic of the Week
By Michael Oxner, October 12, 2003


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This week's topic:
Airport Operations Part 3a: Take-Off

Next we move on to the act of taking the runway for departure. Bear in mind, the majority of this deals with controlled airports more so than uncontrolled. There are a few items to cover off, so let's get to it.

Selection of Runway
    Requesting Another
Taxiing to Position
    Backtracking
    Intersection Departures
        Rules
        Considerations
Take-Off Clearances
    Sequence of Clearance Items
    Immediate Take-Off
    Acknowledgment of Take-Off Clearance
Release From Tower Frequency

Selection of Runway

For the Tower, the selection of the runway is not always simple. There are a few items to consider, the wind being an important one, but not the only one. ATC's Manual of Operations, or MANOPS, section 302 deals with runway selection, so we'll have a look at that.

First, as far as wind speed is concerned, ATC has direction to "assign the most operationally suitable runway most nearly aligned into the wind if the wind speed is 5 knots or more". If it's less than 5 knots, a calm wind runway may be assigned to aircraft using the airport. The wind speed and direction must be stated to aircraft if the runway is not aligned into the wind. The calm wind runway is often determined by factors other than winds, including, but not being limited to, noise abatement, runway length/width, runway lighting/NAVAIDs available, and so on. For example, if the winds are calm and a lot of heavy traffic is expected, the TWR may declare the longest runway as the active runway. Also, TWR may assign one runway to aircraft taking off and landing and assign a different runway to aircraft that remain in the circuit. If you're not familiar with the term "circuit", it's the traffic pattern flown around a runway. I'll go more into that in a future topic.

What if the active runway is not good for you as a pilot? Perhaps the wind has the TWR assigning a shorter runway than what you need. Maybe a 15 knot crosswind component would be acceptable given the longer length of another piece of pavement. The pilot is ultimately responsible for acceptance or refusal of a take-off clearance on any given runway, since his life is the one in the hot seat. In keeping with this idea, there is nothing stopping a pilot from asking for another runway. If anything, it's very much the opposite, pilots being encouraged to make the right choices. So if the active is not acceptable, for whatever reason, ask for something else, Mr. Pilot. And Mr. Controller, part of your job is to get the pilot what he needs as efficiently as possible, where practicable. For pilots, consider the fact that a number of other aircraft may be using the active runway and getting the runway of your choice may pose a delay for you, perhaps even a significant one. Similarly, ATC may see a delay due to other traffic and may suggest an out-of-wind runway that might expedite an aircraft's departure. ATC has a responsibility to advise the pilot of the expected length of the delay, should one be likely. ATC also has direction, again out of MANOPS 302.3, to clearly indicate the wind speed and direction if an out-of-wind runway is requested or suggested.

Remember, the controller may assign a runway under the right conditions, and he may suggest a runway, too. But the pilot has the final authority for acceptance of a particular runway for take-off.

Taxiing to Position

Now that the runway has been selected, and ATC has provided taxi instructions to get you there, the next step is getting out on the runway for take-off. Without authorization, no aircraft is to enter an active runway. The AIP RAC 4.2.5 says so, as mentioned last week. ATC has another phrase in his book, "Taxi to position runway XX". This means, "you can enter the runway, line up on the runway as you would for take-off, but that's it". For ATC, saying "taxi to position behind the landing traffic" is a no-no. Such conditional clearances are specifically prohibited in MANOPS 303.3. Instead, controllers, you wait until the landing traffic has passed before you say, "Taxi to position", or have the aircraft waiting for the landing traffic advise when the traffic goes by. The latter is more of a procedure for real-world in low visibility without an ASDE, since in VatSim, we can always see the aircraft on the runway. There are some limitations to the "taxi to position" phraseology. Read on.

There are also some other rules for ATC. More than one aircraft can be taxied to position at the same time, including more than one on the same runway, and more than one aircraft on more than one runway. If this is done, a sequence must be issued to each aircraft that is not number one (eg: "Taxi to position runway 33 and wait, number 2 for departure. Traffic, Dash 8 departing runway 06").

Also, it is possible to put an aircraft to position on the runway without expressly saying "taxi to position". This is when the take-off clearance is to be issued right away, rather than getting the aircraft onto the runway first, then clearing him to go. I'll say more about this later on.

Backtracking

At many airports, there are no taxiways that run right to the runway threshold. This means the taxiway nearest to the threshold of the runway intended for take-off might be a few hundred, or a few thousand, feet behind where the taxiway meets the runway. The term applied to taxiing on a runway in the opposite direction to that used for take-off or landing is, "Backtrack". Back to the AIP RAC 4.2.8, any time a backtrack is required or desired, a clearance to do so must be obtained from the tower before commencing such a manoeuver. The reason? Not because TWR doesn't want you to do it, but they have to know about it. They might have a limited time to get you out there. If you were to do the backtrack unexpectedly, the TWR may have to pull someone on short final due to the extra time you take on the runway.

Intersection Departures

Right in line with the last section, "intersection departures" can be a useful tool for both pilots and ATC. An intersection departure is one where a taxiway is used that doesn't reach the runway threshold and the pilot doesn't backtrack from there for take-off. He simply taxis on to the runway, turns in the direction of take-off, and away he goes. There are some rules for these, and some considerations, too.

First off, the rules. ATC may suggest an intersection departure, and this is usually meant as a way to get an aircraft airborne sooner. For example, if the runway to be used requires entry into another runway to get to the threshold but another taxiway will get the aircraft onto the runway without crossing the other one, this could certainly make a departure quicker. Halifax International (CYHZ) has such a configuration, among many, many other airports. In this case, Taxiway Echo will provide an aircraft with 7,800 feet of the 8,800 feet available -- enough for most aircraft in many conditions, especially if you're only flying a C172. In fact, that's one of the rules for ATC, in MANOPS 334.5: They are supposed to provide the pilot with the runway length remaining from the intersection they suggest the departure from. While most VatSim ATC online don't have this information available to them, real world controllers will have a chart showing these distances. When issuing instructions to taxi to position at an intersection, remember, ATC guys, to specify that. "Taxi to position Runway 24 at Echo". Take-off clearance must be worded similarly ("From Echo, cleared take-off runway 24"). Wind speed and direction should also be clearly indicated to the aircraft. Why? Read on.

The considerations are numerous, but many include common sense. Those that don't include common sense often include thoughtful extensions to common sense. Runway length available is the most obvious one. A good pilot knows how much runway he can expect to use on take-off, including getting over obstacles at the far end. He also considers things like an aborted take-off. If he has to abort prior to lift off, does he have enough runway to decelerate to a stop without overrunning the pavement? How about winds? What about runway surface contamination? If there is ice on the runway, it would greatly increase the stopping distance required for a rejected take-off. Similarly, runway slope has an effect on the runway length required, as does air temperature and air density. When ATC suggests an intersection departure, or when you're considering one as a way to get off the ground quicker, make sure you know if there is enough runway remaining for your circumstances.

Take-Off Clearances

There are a few things to take-off clearances that some don't quite get right in our VatSim world. What to say, in what sequence to say it, and for pilots, what requires a readback. Some of the information contained in the average take-off clearance includes things like wind, departure frequency, traffic information, instructions and the actual take-off clearance. How about looking at some of the other things and when they're required?

Sequence

In the take-off clearance, the last thing said is, "Cleared for take-off runway 24". The reason is simple: If a pilot eager to get airborne hears the magic words, "Cleared for take-off" first, then he may not register the rest, thinking, "yeah, yeah, blah, blah, blah, hit the throttles and then the blue sky". Anything after the magic words tends to get ignored. MANOPS comes into the picture again, this time 336.12 is the reference:

Issue a take-off clearance in the following form:
1. Aircraft Identification
2. Unit identification if required
3. Special information, such as a hazard or obstruction
4. Control instruction, such as a turn after take-off
5. Wind information if required
6. CLEARED FOR TAKE-OFF RUNWAY (number) - if from the threshold or - FROM (name of taxiway or runway intersection), CLEARED FOR TAKE-OFF RUNWAY (number).

I think everyone understands aircraft ident. The unit identification is simply the name of the unit you're working. This is only required if the take-off clearance is the first transmission you make to the aircraft. If you're already in contact with the aircraft, having told him to wait or having taxied him to position, this is not needed. Only on your first communication with an aircraft are you supposed to say the name of your unit.

Special information includes traffic, weather related information, bird activity, and whatever else you can think of that might affect a take-off run or the early part of a climb out. If there's a lot of static conditions, like runway surface conditions and so forth, these are best provided with taxi information, or better yet, on an ATIS message. Try to keep this short and concise. The fewer words used to get the point across, the better.

Control instructions would, as the text above reads, include such phrases as, "left turn out as soon as able", "climb runway heading til further advised", "right turn out approved", and so forth. Anything required for control to get an aircraft out of the way faster, or to keep him out of the way of someone else goes here.

MANOPS 336.11 tells us that we only really are required to give wind information if the wind speed is 15 knots or greater. Many people give this information anyway, and I don't see it as a fault. As a pilot, I like to hear it with a take-off and landing clearance even if it is less than 15 knots.

Then, the words we've all been waiting for, "Cleared for take-off runway XX". Like I said, the last thing to be said in the take-off clearance is the take-off clearance. Even when issuing a T/O clearance from an intersection, the name of the intersection is said first, then the words. For example, "From Delta, cleared for take-off rwunay 24". I want to mention another thing: I was raised in ATC in the real world to avoid the term "take-off" unless using it with the words "cleared for". Any other time you want to talk about take-off to an aircraft, use another term like "departure". The term "take-off" should be left as a sacred phrase so that someone doesn't misinterpret what is being said as authority to take-off.

Immediate Take-Off

The above phrase is important enough to give more than just a casual mention. When you're cleared for take-off, you are expected to taxi to position, prepare for the take-off roll, and commence the take-off within a reasonable period of time. If you've not completed your checklists or you don't have your weight and balance figures from dispatch, or whatever, advise the tower before you take the runway. They may have traffic on final, or perhaps waiting in another taxiway that is ready to go.

Having said all of that regarding a normal take-off clearance, there is an expression, highlighted as the sub-section title above, that ATC will use if they think they have enough space to get you out there. The term "immediate" is just that: You have to be able to get on the runway and start the take-off roll right away, all in one continuous motion. No slow taxiing out, no stopping on the runway while you finish something you're doing, or anything like that. You just get out there and go if you accept such a clearance. Normally, ATC will ask ahead of time, to let you know that an opportunity is coming for you. "ACA123 are you able immediate?" If you're not, say, "no." If you are, say so, and and get ready to go when he gives you the word.

Another way this comes up sometimes is when ATC sees an opportunity but didn't see it in enough time to check to see if you're ready and able. He might say something like, "Oscar Oscar Lima, winds 240@5, cleared immediate take-off runway 24. If unable, hold short and advise". Do as he says. If you're not ready, don't enter the runway and let him know. If you are, get a move on, get out there and go.

From an ATC point of view, controllers have to remember some issues about immediate take-offs, too. The average Cessna 172 can be readied for take-off fairly quickly. Given their light weight, small size and relative simplicity in the cockpit, the Skyhawk can taxi out to position, firewall the throttle, roll and get airborne in a fairly short period of time. A B747 on the other hand, needs time to spool engines up to get enough thrust to roll (maybe not so much time if you catch him before he comes to a stop), time to manoeuver the big airframe onto the runway and line up, and then a fair amount of time to spool the rest of the way up to take-off power and move the 800,000 lb hulk down the runway to take-off speed. See what I'm saying, controllers? You have to consider aircraft type, aircraft position on the field, if he's still moving or at a complete stop, runway conditions, whether or not the aircraft will need a backtrack for take-off, etc. All of these have to be considered before you hang you virtual license out there and suggest an immediate take-off. Any licensed ATC in a real world tower will also tell you he evaluates the response from such a question, too. If a pilot responds with, "Say again?" or, "How much time do I have?" the controller will likely say, "Disregard. Hold short, traffic landing." If a pilot answers with a waver in his voice, it should raise a red flag as to whether he can actually do it, so you may decide to cut the idea off before he gets out there. You're working with a small window of opportunity if you need an immediate take-off, so both you and the pilot have to be ready for this to work.

Acknowledgment of Take-Off Clearance

One last word about take-off clearances: Like any other clearance, it should be acknowledged. The simplest form of acknowledgment includes merely the callsign of the aircraft. It's quite typical for IFR aircraft, in particular, to readback the take-off clearance (not normally including the winds) with any other instructions issued with it. This gives a confirmation of what was said, and an opportunity for the TWR controller to listen to a readback to ensure the correct aircraft heard the clearance, the correct runway is being used, and the instructions issued were received correctly.

Release From Tower Frequency

The AIP RAC 4.2.9 has a couple of things to say about this. Unless otherwise advised, pilots normally don't require permission to change from the TWR frequency, once clear of the control zone. It also says that pilots should not request release from this frequency or or report clear of the zone when there is considerable frequency congestion. Pilots should, where practical, monitor the tower frequency until at least 10 NM from the control zone.

In the case of an IFR flight, the tower will normally advise the aircraft when to contact the IFR ATC unit. Typically, the instruction to contact the IFR unit will be included with the take-off clearance. For example, "CVA822 contact Moncton CTR 124.4 when airborne, winds 240@10, cleared take-off runway 24." This has worked successfully for me in the real world as a controller, but in VatSim, I've had a few problems. First, it says, to contact CTR when airborne. That means, "for now, monitor my frequency, and change to the CTR when you're in the air." So don't tune me out while you're sitting on the runway. In fact, start your take-off roll, rotate, get airborne, and sometime during or after the process of tidying up the aircraft's gear and flaps, tune the radio and make contact with CTR or DEP. The key to this is spending as little time on the runway as practicable. Especially if an immediate departure is required. Taking the time to tune a radio before you roll could lead to a major problem, since you take extra time on the runway, and TWR can't reach you any more.

Sometimes the TWR will have reason to keep a departing IFR aircraft on his frequency after take-off. It is perfectly acceptable to do this, but it should be coordinated with the CTR, first. Perhaps there is traffic near the departure end, or whatever. If it is necessary, it might be a good idea from a TWR point of view to remind the aircraft, "stay on my frequency after departure, cleared for take-off runway 06." Then, when he's clear of the traffic, say, "contact Gander Center now on 132.1."




Well, thanks for reading. I hope I've answered a few questions, explained a few things to pilots and controllers alike, and maybe helped out a bit with take-off clearances. There will be more to come as asides in future topics, but I thought some of these would be better left to later so they can be kept in context. If there's anything you feel was left unsaid, or perhaps something you disagree with, by all means, e-mail me. If a correction is to be made, I'll make it, or perhaps I can help clarify something that was or wasn't said. My e-mail address is moxner@nbnet.nb.ca.