Monday, July 14, 2008

Cleared to blog!

"Cleared."

This is the word that inspired me to start this blog. It's a word that is misunderstood and highly overused in the ATC flight simulation community.

I was just piloting in a session wherein the virtual controller running the tower was clearing people for everything. Cleared to taxi. Cleared to an altitude. Cleared to turn base. Cleared to extend downwind. Cleared to turn to a heading. Cleared to park at the ramp. It was making me nuts. He was doing a great job of running the pattern, but his phraseology was killing me.

"Cleared" may only be a short arrangement of 4 consonants and 3 vowels, but it has killed quite a few people when it was used improperly. The 1977 Tenerife crash of two 747s - the worst aviation disaster in history until 9/11 came along - was caused because one pilot thought he'd been "cleared' for takeoff. It's a word that is not used lightly.

As an air traffic controller, when you clear a pilot to do something you are taking their life in your hands. When you clear someone for takeoff, you're telling them that you've ensured the runway is free of other traffic and that no one's going to land on their head. When you give someone an IFR clearance, you are promising them that you are going to keep them separated from other aircraft, terrain, and obstructions. When you clear someone for an approach, you are telling them you've ensured they've got the proper wake turbulence separation between the aircraft ahead of them and are not going to conflict with other aircraft landing at the airport on other runways.

It's a lot of responsibility, packed into one little word.
To see it used so wantonly by virtual ATC-ers online makes me cringe a bit. Obviously, those folks don't know any better and I don't hold it against them. I fully realize it's just a game, but it is based on a serious occupation. So, I do want to make an attempt to set the record straight.

"Cleared" is primarily used in four major instances within the spectrum of ATC phraseology. These four are listed below, along with their proper usage.
  1. Cleared for takeoff.
    This phrase always comes at the end of a takeoff clearance, not the beginning. Remember, you're talking to a pilot. They're sitting at the hold short line, revved up, ready to go, and the only thing holding them back is you clearing them for takeoff. Once they get that clearance, their brain switches from "listen mode" to "let's-get-this-baby-in-the-air" mode.

    What you say: "N123, cleared for takeoff, runway 20. Wind 230 at 10, gusting 25. After departure fly heading 230."
    What the pilot hears: "N123, cleared for takeoff, runwa.... blah blah blah blah..."

    That's why the takeoff clearance comes last. You want to make sure the pilot's attention is still focused. By making them wait for that highly important clearance, you're making sure they have the wind and departure info they need.

    A good way to remember this would be to tell yourself to think backwards. Go from least important to most important. For example:

    "N123, wind 230 at 10, gusting 25. After departure fly heading 230. Runway 20, cleared for takeoff."

  2. Cleared to land.
    This follows the "think backwards" principle as well, in that the clearance comes last. I've heard people throw all kinds of junk into landing clearances. Altimeters. Weather reports. What you need is the following:
    • Wind
    • Relevant traffic
    • Wake turbulence (if applicable)
    • Runway
    • Clearance

    Example: you've got a Piper 789 turning base for runway and an American 737 on final.

    "Piper 789, wind one two zero at four, number two following Boeing 737 on one mile final, caution wake turbulence, runway two zero, cleared to land."

  3. Cleared to [destination]
    Used in this context, "cleared" is the magic word that transforms a VFR airplane into an IFR one. Up until a pilot hears the words "Cleared to..." he'd better stay clear of clouds and above 3 miles visibility, because he is considered VFR and better be operating under VFR rules.

    Departing aircraft:
    Typically in FS X, the departing pilot will input a flight plan into the text chat box and then call Clearance Delivery:

    FP|N123|LJ45/A|230|KTMB..KBCT..KMCO

    You don't want him rocketing up to twenty three thousand right off the bat. Typical procedure is to tell an aircraft to expect a 10 minute delay before reaching their requested cruising altitude. That way, if you lose radio comms, you can expect the airplane to climb after the 10 minutes have passed if they're not talking to you and continue on their flight plan, giving you enough room to clear a path. The proper phraseology for this would be:

    "Learjet 123 is cleared to Orlando International as filed. After departure climb and maintain three thousand. Expect flight level two three zero one zero minutes after departure. Departure frequency will be 123.12. Squawk 1234."

    Airborne aircraft: Radar controllers can also give IFR clearances in the air. This is commonly called an "IFR Pickup". Let's say you have a pilot that was operating VFR and has now encountered bad weather conditions. If they're landing at an airport in your airspace, you can issue them a local IFR clearance.

    This local clearance is typically comprised of four things:
    • A clearance limit (typically an airport or fix)
    • An altitude
    • A heading
    • A reason for the vectors

    So, if Cessna 456 has encountered some haze and wants an IFR pickup to KTMB, all you'd need to say would be:

    "Cessna 456, cleared present position direct Tamiami airport. Maintain four thousand, fly heading two five zero. Vectors ILS runway niner right approach."

  4. Cleared approach
    The previous three were all used in the tower environment. "Cleared approach" is used exclusively within the radar environment to clear an IFR aircraft for an instrument or visual approach. For all but the visual approach - where they just need to report the airport or preceding traffic in sight - you'll need to issue the following:

    • Distance from a point on the approach (this can be the airport, the initial approach fix, the final approach fix, etc.)
    • A heading to fly that is both:
      • Within 30 degrees of the approach heading (45 degrees for helicopters) .
      • Will allow them to intercept the approach at least one mile outside of the final approach fix (three miles if the field is ceiling is low).
    • An altitude to maintain that is:
      • Above your Minimum Vectoring Altitude
      • Will realistically allow them to intercept the glideslope of the approach.

    An example would be:

    "American 123, seven miles from Miami Airport, fly heading zero six zero, maintain one thousand seven hundred until established on the localizer, cleared ILS runway niner approach."

    Approaches require a whole blog post unto themselves, so you'll have to wait for the full story there. There's a whole set of rules and things that apply here.
  5. Other uses of "cleared"
    There are few other uses of "clear", but these are not nearly as widespread as the previous four. For instance, if you're a VFR aircraft requesting transition through Class B airspace, the controller would permit you access by saying "N123, cleared into Class Bravo." But you'll hear this far less than you would the other examples.
I will be expanding on all these topics and more as the blog goes on. ATC is simply a deep subject, much of which needs explanation for newcomers to see why it makes sense. I hope you'll return for some more.

Please feel free to ask any questions about things I post on here. Comments are always welcome!

2 comments:

Jeff said...

move this to MAIN

Towerboss said...

It's actually gust not gusting.

Wind one two zero at one zero gust to two zero.