Wake turbulence avoidance and ATC

On Thu, 18 Dec 2003 11:01:37 -0500, Peter R.
wrote:

A couple of days ago I flew into Logan Airport (Boston, MA, USA) in a C172
for an Angel Flight. Taxing to the departing runway, we were behind a B767
and a DC9 (in that order), with several other large airliners behind us.

I noticed that there seemed to be no wake turbulence delay for the DC9
behind the B767, as he was cleared for TO less than a minute after the B767
departed.

Tower then positioned me on the runway, and again, less than a minute later
(after awaiting a crossing runway landing), gave me a 90 degree right turn
after takeoff heading, cautioned wake turbulence, then cleared me to go.

My question has to do with the ATC's wake turbulence procedures. At the
class C airport where I am based, I constantly hear about the 3 minute rule
from ATC. In other words, if I am departing from an intersection mid-
field, tower will say that they are required to make me wait three minutes
for wake turbulence avoidance (unless I wave it, which I normally do not).

In the case of Boston's tower, did her "wake turbulence caution" and/or
right turn heading allow her to clear me sooner than the three minutes?

BTW, the DC9 ahead of me took at least three quarters of the runway to lift
off, then turned left. When I departed, I dropped a notch of flaps to
lift off very quickly, climbed a few hundred at Vx as per the obstacle DP,
then turned the 90 degrees right as per the instruction to be well away
from the previous two aircrafts' wake turbulence.

On the times I've been to BOS, it seems routine for tower to vector small
a/c on a different heading than the large a/c. When I've been in that
position, and visualizing the wake, I've never had a question that I would
be able to avoid the preceding a/c's wake by making my turn out as
directed.

If I had, I would have requested to delay my departure.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

David Rind wrote:

You are clearly right about this

Thank you for the gracious reply.

-- I was thinking in terms
of rate of climb, not angle of climb. That said, I would
still be more interested in making an early turn than in trying
to climb quickly and would always ask for an early turnout
in this situation....

In this particular case (taking off right after a jet), at Vx you will reach
turning altitude in less distance and more time, both of which work in your
favour:

- less distance means that you are at a safe turning altitude further away
from the point where your climb path would intersect the jet's climb path

- more time means that the the jet's wake vortices have had more opportunity
to dissipate by the time you turn.

Or, to put it the other way, if you climb at Vy you will arrive closer to
the jet's climb path, sooner, before you reach a point when you can turn.

On the other hand, if there were a jet waiting to take off behind me and I
wanted to get out of the way as soon as possible (i.e. ATC says "right turn
to heading XXX as soon as safely able"), then Vy is the better choice, since
I want to get to turning altitude in the least time.


All the best,


David

Newps wrote:

Don't confuse taking off at an intersection with taking off at the end.
The three minutes applies to an intersection takeoff only.

OK, very good. That answers my question.

--
Peter










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David Rind wrote:

Were you in IMC such that the DP altitude mattered to you?
I was picturing this happening in visual conditions where you
could start maneuvering (as long as Logan permitted) much
sooner.

It was VMC but the tall control tower was close to my turnout heading
and it was night time. We were departing 22 Right with a turnout to the
west.



--
Peter










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Nomen Nescio wrote:

snip
Seems like the result speaks for itself. No problems, right?

Sure, there were no problems but my question was not really about my
plan as much as it was about ATC procedure. Newps corrected my
understanding of ATC's wake turbulence procedures.

As I'm sure you know, and others will probably point out, It's your
show. If you don't like the instructions from the tower, don't do it.

I agree. I am fully aware of my PIC card and will play it if needed,
but I also know that orderly operations at larger airports require me to
think and fly a little differently. This is why, at least at this
level of my experience, I choose to fly into BOS with an instrument-
rated co-pilot.

I'm sure they'd rather have you tie up the runway for a couple of
minutes than have you close it down for a day to clean up the wreckage.

Rather than tie up the runway, ATC would most likely instruct me to pull
to the opposite taxiway and wait, then wait and wait some more. There
were several airliners behind me and had I asked for a wake turbulence
delay, they would have been happy to oblige... by sending me to the
corner of the airport until all traffic subsided sometime a few hours
later.

So you do Angel Flights? Maybe I need to re-evaluate my opinion of you.

Don't change your opinion on account of this. About 95% of my flying
these last several months has been for Angel Flight Northeast and Angel
Flight East. In my opinion, there is no better way to get mission-
oriented, cross country and busy airport experience, all while providing
a much-needed service to those who are less fortunate. Call me what
you will, but soon after receiving my PPL I got bored of the $100
hamburger flights.

Damn, are we both New Englanders, Too?

Based out of Syracuse, NY. Where are you?


--
Peter










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Peter R. wrote in message ...
snip
My question has to do with the ATC's wake turbulence procedures. At the
class C airport where I am based, I constantly hear about the 3 minute rule
from ATC. In other words, if I am departing from an intersection mid-
field, tower will say that they are required to make me wait three minutes
for wake turbulence avoidance (unless I wave it, which I normally do not).

In the case of Boston's tower, did her "wake turbulence caution" and/or
right turn heading allow her to clear me sooner than the three minutes?

It's been a few years since I was based at a Class B airport, but I
seem to recall that the 3 minute rule applied only if you were making
an intersection takeoff behind a departing big boy.

If you're departing from the end of the runway, ATC doesn't have to
wait 3 minutes. At that point, it's up to you to decide when to go.

A small single taking off right behind a big jet was routine at PHX.
The procedure was the same as you described. Climb hard and turn 90
degrees ASAP. The one thing I would caution you about would be the
jet-wash from the departing jet. Although the wake turbulence from
the wings doesn't start until the jet lifts off, those jet engines can
really churn up the air as it rolls down the runway. For this reason
I usually stuck to a Vy climb to give me a better margin over the
stall speed should I encounter some really churned up air. The
turbulence from the airliners was worse from those with high, fuselage
mounted engines (i.e. DC-9, 727). It was also worse when the wind was
dead calm.

John Galban=====N4BQ (PA28-180)

David Rind wrote in message ...
David Megginson wrote:
David Rind wrote:

Not answering your actual question about the clearance, but for
what it's worth, I would not have tried to climb out at Vx. You
have no hope of outclimbing a jet,

It's not that far off -- I think (but am not certain) that a
fully-loaded DC-9 has a best climb angle of around 650 ft/nm, while a
small single-engine plane will manage something like 400-600 ft/nm at Vx
depending on horsepower and load. Of course, the DC-9 has a much better
climb *rate*, but that's not the concern here [...]

I could be wrong, too, but I think even a loaded DC-9 can manage at
least 1000-1500fpm... and might have to do so for noise abatement
around the airport.

I've heard that's why cloud clearances down around us VFR planes are
1000' above and 500' below. The extra space above is needed because
an airliner is far more likely to be climbing out at high fpm... but
descends at a slower rate for passenger comfort and ILS landings.

Kev

Nomen Nescio wrote:

So, what? I'm supposed to think less of that because you reap some
personal benefit from it. I'm really not THAT much of an a-hole, believe
it or not.

I am starting to believe that you might not be.

How did you get involved with that?

I recall reading about Angel Flight in this newsgroup back before I had
my instrument rating. After some quick research, I found the websites
of the two local AF groups that serve the northeast US, then sent them
both an email asking what the requirements were to join.

300 hours plus an instrument rating, as well as 25 hours actual IMC (I
think that was the number).

That gave me the incentive to get my instrument rating sooner rather
than later. After receiving my rating I contacted them again. This
time both groups sent me a one-page application. I sent it back with
copies of the last few pages of my logbook and proof of aircraft
insurance. Upon verification (a couple of days), I was notified that I
could fly missions for them. AFNE also required I attend a two hour
introductory meeting to review the organization.

Angel Flight Northeast, based in Lawrence, Mass:
http://www.angelflightne.org/contact1.htm

Angel Flight East, Based in North Philadelphia:
http://www.angelflighteast.org/

And how does it work? I'm interested in some details.

AFNE publishes open flights on their web site, approximately 6 to 12 per
day. AFE sends out an Excel spreadsheet via email once a week, with
only about 1 to 2 per day listed. You look through the list of open
flights, then choose the flight you want (on AFNEs website) or email AFE
the flight you want. Both groups list flights up to two months in
advance.

Date and day of flight, number of passengers, departing and destination
airports, weight of passengers and luggage, and planned arrival or
departing times are included in the list to assist the pilot in choosing
a flight. Fly one a year or several a week, depending on your schedule.
I try to fly at least one per week, but this NE winter has been less
than cooperative.

When you meet the passengers, you ask them to sign a liability form that
must be faxed to the AF office before departing. Most FBO receptionists
will fax this for you. Then fly.

After returning home, fill out a 1/2 page mission report detailing your
estimated expenses and send it in. AFNE's form can be filled out on
their website. About a week later, you receive an official tax
deduction letter identifying your charitable donation.

Occasionally, you receive a postal letter containing pictures of the
little child and/or family you flew, along with a heartfelt thank you
note. To know you made a small difference in these people's lives is
the best part (for me, anyhow).

Being based in Mass., you would find a lot of nearby flights.

Both groups also send out requests for pilots to fly transplant patients
on a moment's notice. Pilots do not have to volunteer for these if they
do not want to be on call, but those who do have to be ready to fly at a
moment's notice.

I signed up for a few, but presumably due to the slow speed of my
aircraft, I have never been called. The thought of flying someone to a
distant city for an organ transplant is definitely exhilarating.

Oh, a New Yorker......that explains some things.g

Night and day when comparing CNY to the City. Many central NY'ers
cannot stand the congestion of the City, and many NY city folks have
never seen a cow, corn stalk, or stars in person. I have lived and
worked in the City, but prefer the slower life of the rural countryside.

A friend and 3 passengers died over Northhampton when a skydiver
bounced off his stabilator at 3500 ft. a few years back. The
skydiver lived and sued my friends wife for the "emotional
distress" he suffered.

Yes, I am familiar with that accident. I think about it every time I
see a parachute symbol on a sectional chart. Sorry to read that it was
a friend of yours. To read that the skydiver actually sued the estate
makes the accident even more tragic. I hope he didn't win anything but
I won't be surprised if you tell me otherwise.

Best regards,

--
Peter










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Night and day when comparing CNY to the City. Many central NY'ers
cannot stand the congestion of the City, and many NY city folks have
never seen a cow, corn stalk, or stars in person. I have lived and
worked in the City, but prefer the slower life of the rural countryside.



Actually we do see the stars here in the city... but only during blackouts.

"Peter R." wrote in message
...
300 hours plus an instrument rating, as well as 25 hours actual IMC (I
think that was the number).

AFNE's literature does say 25 hours of IMC, but they told me it was a
typo--they merely require 25 hours of total instrument time. (Otherwise, I
wouldn't have been able to fly for them yet.) I'd guess that most
recreational pilots don't get more than a couple of hours of IMC per year.

--Gary