Aviation Topic of the Week
By Michael
Oxner, February 29, 2004
This week's topic:
IFR Flight Example, Part 5: En Route
Last week, our pilots of the Beech 200 Super KingAir
finally got airborne. We'll continue the example flight beginning this week
with the enroute phase of flight.
Review of Situation
Requesting Altitude Change
Evaluating the New Altitude
New ATC Unit
Turbulence Encountered
VFR Descent
Visual Passage
Further En Route
Review of Situation
Our pilots departed CYJT, left the MF area, and called in to Gander
Center (CZQX). They were radar identified by Gander, passed their traffic
in cloud, and were cleared up to their flight planned altitude of 14,000.
So far, everything is going as planned. Fuel burn is acceptable, estimates
for various points have been calculated (even though the position reports
are not required) and everything seems hunky dory.
Requesting Altitude Change
When they reach the planned true airspeed of 260
knots, they notice a groundspeed reading on the DME of 240 knots, which
is about 20 knots faster than planned. This leads the copilot to believe
that the wind forecast may be off a little. If that is true, and the winds
aloft are not as strong as forecast, perhaps a higher altitude may offer
better fuel economy after all. After a brief discussion, the pilots decide
to change altitude, and try out 16,000 to see if the winds are better there.
Since they are IFR in Class B airspace at this point, a clearance must be
obtained prior to the climb.
FART: "Gander, Alpha Romeo Tango, request climb
to one six thousand."
CZQX: "Alpha Romeo Tango maintain one six thousand."
FART: "Alpha Romeo Tango out of one four thousand
for one six thousand, thank you."
CZQX: "Alpha Romeo Tango, roger."
A few minutes later...
FART: "Alpha Romeo Tango level one six thousand."
CZQX: "Alpha Romeo Tango, roger."
Evaluating the New Altitude
Now that the new altitude is reached, the pilots will evaluate it. The
first conditions that are looked at include the immediate things like the
ride, the conditions outside (are we in cloud, or riding the tops which are
likely to give turbulence, etc.), is there icing, and that sort of thing.
Since the aircraft would lose some speed to make the climb, the pilots must
wait a couple of minutes to accelerate and get the new groundspeed readout
from the DME. If only that darned RNAV were working, the winds would be available
right on the display...
If you remember back to the wind forecast in the Preflight briefing (part 1 of this
series), the winds at 12,000 were forecast to be about 40 knots on the
nose, and those at 18,000 (FL180) were forecast to be significantly higher,
blowing from the southwest at about 75 knots. This is why the altitude of
14,000 feet was chosen: to try to get as high as they could without getting
into the really high winds. Well, the pilots notice the groundspeed readout
is lower than it was a 14,000 feet. When they level off at 16,000 and accelerate
back up to their planned true airspeed of 260, the groundspeed shows 185.
Disappointed, the copilot brings this to the captain's attention. Such a
shame. They're in the clear at 16,000, so there's no icing, and the ride
is good. The decreased speed means that if they stay there and the winds remain
somewhat constant, their elapsed time enroute will increase by a few minutes.
This is determined by approximating the distance remaining and comparing the
two speeds they did. We'll say the distance remaining when the calculation
is done is 250 NM. At 240 knots groundspeed, this would take 1 hour and 3
minutes, written as 1+03. At 185, this will take 1+21. This means an additional
18 minutes of flight, which means another 18 minutes of fuel burnt. The decision
is made to return to 14,000 feet.
FART: "Gander, Alpha Romeo Tango."
CZQX: "Alpha Romeo Tango, Gander."
FART: "The winds are much stronger up here, we'd
like to return to one four thousand."
CZQX: "Alpha Romeo Tango, roger. Standby..."
Behind the scenes, Gander is coordinating the altitude change with
the next ACC, which is Moncton. If you look at the charts, considering
that the pilots have flown about 65 NM, they are getting quite close to
the boundary with Moncton. Remembering that our NOTAM sheet included one
about the Sydney radar being off for maintenance, the delay in getting
the clearance might be attributable to that.
CZQX: "Alpha Romeo Tango, descend to one four
thousand."
FART: "Alpha Romeo Tango in descent to one four
thousand."
CZQX: "Alpha Romeo Tango, roger. Radar service
terminated, report level with Moncton Center on one one eight six. Good
day."
FART: "We'll call Moncton on one eighteen six
when level at one four thousand, Alpha Romeo Tango. Thanks for your help."
New ATC Unit
The pilots' situation has changed in a couple of ways, and neither of
them terribly significant, if at all. First, the pilots will now be talking
to Moncton Center instead of Gander. What impact will this have? Nothing,
really. The last transmission from Gander included a phrase which does have
some importance to our pilots, though. "Radar service terminated."
This means that our pilots must now make position reports to ATC, since
they are no longer inside radar coverage. The copilot takes out the paper
with the flight plan and the estimated times over the compulsory reporting
points as determined after take-off and verified after leveling off. He
tells the captain prior to calling Moncton the estimate for YQY VOR, and
that time is 1632z. They are reaching 14,000, so as instructed by Gander,
they make their level call with Moncton Center (CZQM).
FART: "Moncton Center, good afternoon. KingAir
Foxtrot Alpha Romeo Tango with you level one four thousand. Estimating
Sydney at one six three two."
CZQM: "KingAir Foxtrot Alpha Romeo Tango, Moncton
Center, good day. Sydney altimeter is two niner five four."
FART: "Two niner five four. Alpha Romeo Tango."
Again, behind the scenes, ATC has recorded the pilot's estimate for future
reference. In a non-radar environment, ATC bases separation on time, among
other things, so they have their own estimates for each aircraft at each
point of importance. If ATC's estimate is close to the pilot's estimate, nothing
more will be said. If the pilot's estimate is substantially different from
ATC's, ATC will often ask the pilot to verify his estimate, typically asking
for a DME or other type of position report, while he verifies his own estimate,
too.
Turbulence Encountered
Cruising along, still northeast of YQY, the pilots have NAV1 tuned to
YJT's VOR, and NAV2 now tuned to YQY VOR. Setting the radials for the airway
from each of the NAVAIDs, the pilots confirm they are, indeed, on course.
The ride starts to get a little choppy, starting with intermittent light
chop. Knowing the boss in the back likes a comfortable ride, the pilots begin
to talk about trying another altitude. As the chop turns from intermittent
to continuous, and then light to moderate, the talk becomes more serious.
They've already experienced the winds at 16,000, and that was not acceptable.
What about 12,000? Perhaps that's better. There's one easy way to find out.
FART: "Moncton, Alpha Romeo Tango. We're getting
continuous moderate chop here at one four thousand. Do you have any ride
reports at altitudes below ours?"
CZQM: "Standby. Coast Guard three hundred, Moncton."
CTG300: "Moncton, Coast Guard three hundred."
CZQM: "What's your ride like?"
CTG300: "In the clear and smooth. We're just coming
up on Sydney VOR now."
CZQM: "Alpha Romeo Tango, an eastbound Dash eight
just west of Sydney calls the ride smooth at one three thousand."
FART: "Roger, we'd like to request one two thousand."
ATC may not have had any traffic through the airspace you're inquiring
about, so you may be the guinea pig. But it never hurts to ask.
VFR Descent
Looking at the situation, the pilots know there could be a delay getting
a clearance to 12,000. They are currently only about 20 NM from YQY, and
they know a Dash 8 coming the other way, just about over YQY now at 13,000.
Since they're well above the cloud deck below them, the copilot immediately
suggests to the captain a VFR descent. This is a procedure
whereby an aircraft wishing to change altitudes but can't because of IFR
traffic may make the climb or descent in accordance with Visual Flight Rules,
or VFR. The requirements are the same as if the aircraft were flying VFR
to begin with: see and be seen. For this manoeuver, the IFR clearance is
valid until leaving the first specified altitude, and valid again upon reaching
the new altitude assignment, and the pilot is to provide his own separation
from terrain and other aircraft (which includes wake turbulence ) separation,
while between the two altitudes just as if he were VFR. ("Air Canada
123 descend to 4,000. Make descent from 8,000 to 6,000 VFR. Traffic is...")
The procedure must be requested by the pilot and the weather must permit
such a move (ATC has no way of policing this, since they don't know exactly
what the weather is where the pilots are). ATC may deny the manoeuver. There
is one more point that is a consideration that the captain promptly reminds
the copilot of: visual climbs and descents are not an option in Class A
or B airspace, since ATC must provide IFR separation within both of these
classes of airspace. VFR flight is not allowed, so the visual climbs and
descents are not, either. It looks as though the altitude change will have
to wait. Moncton responds to the altitude change requested in the last transmission.
CZQM: "Alpha Romeo Tango, we'll have to wait
until you pass the Dash. I don't have radar, but the Dash is turning the
corner at Sydney to head toward Stephenville. If you happen to see him
go by, let me know and that'll get you descent earlier. What's your DME
now?"
FART: "Alpha Romeo Tango will report visual passage.
We're at seventeen DME."
Visual Passage
Visual Passage is a way of speeding up altitude changes in situations
such as the one developing now for our pilots. ATC can use radar to prove
"tail-to-tail" and drop one aircraft through the altitude of the other as
soon as the targets no longer overlap on radar, even though he hasn't reached
the separation normally required for the airspace concerned (5 NM or 3 NM
in a terminal environment). There are some other minor conditions to go
along with this, but they're easily met so I won't go into them here. With
the lack of radar coverage in our example flight, Moncton will have to resort
to another form of "tail-to-tail", a procedural one. To ATC, the
term "procedural" means the separation standards to be applied are non-radar.
Because there is no direct way to get a picture of what is happening, ATC
must rely on reports from aircraft to build the picture. These reports are
used to prove that separation exists (or if it does not) to allow ATC to
provide aircraft with clearances to do what they want. In this case, the
first separation standard that will be met, given that these aircraft are
opposite direction, will be the 5 DME standard. For this one, the aircraft
must pass each other, and then make DME reports that indicate the aircraft
have passed and are at least 5 miles apart. The outbound aircraft must also
be at least 15 miles from the facility, which may pose further delay in
this situation. If RNAV reports such as those from GPS are used, they must
still be 5 miles apart, but there is no requirement for the outbound aircraft
to be 15 miles from the common reference point.
Since they are both in clear air and on the same airway, they stand
a good chance of seeing each other. Despite the fact that the reports being
made are based on visual observations, this is not the same as visual separation.
This is merely proving that aircraft have passed, and since ATC doesn't
protect airspace behind an aircraft, all he has to do is prove that these
two have passed. The visual report will accomplish that, but ATC needs both
aircraft to report passage or visual passage can't be used. (If both are
in Class A airspace, they must be separated by no more than 2,000 feet.)
Very technically speaking, the concept is to see the aircraft out the window,
so a report of passage based on TCAS isn't what ATC is looking for. TCAS may
be used to help spot the traffic, though. In either case, depending on how
you word your message, ATC may not know you have reported visual passage based
on TCAS observation. While none of this has been flight checked the same
way ATC's ground-based radars are, I wouldn't advise this use of TCAS, personally.
Now we continue the radio sequence with the following transmissions:
CZQM: "Coast Guard three hundred, traffic is
a westbound Beech 200, just reported seventeen DME northeast of Sydney
at one four thousand. Report visual passage."
CTG300: "Coast Guard three hundred, wilco."
Some time passes...
FART: "Moncton, Alpha Romeo Tango, I see a red
and white Dash eight passing beneath us now."
CTG300: "Moncton, Coast Guard three hundred also
has visual passage with the KingAir above."
CZQM: "Alpha Romeo Tango, descend to one two thousand."
FART: "Alpha Romeo Tango out of one four thousand
for one two thousand. Thank you."
CZQM: "Alpha Romeo Tango, roger."
Further En Route
In the not too distant future,...
FART: "Moncton, Alpha Romeo Tango with a position
report."
CZQM: "Alpha Romeo Tango, roger. Go ahead."
FART: "Alpha Romeo Tango over Sydney at one six
three three, leveling at one two thousand IFR. Estimating COPAR at one
six four eight, Halifax next."
CZQM: "Alpha Romeo Tango, roger. Halifax altimeter
is two niner four three."
FART: "Halifax two niner four three, Alpha Romeo
Tango."
Some time later,...
CZQM: "Alpha Romeo Tango, Moncton, squawk ident."
Again, no need to reply, as operating the IDENT feature will
suffice as a reply.
CZQM: "Alpha Romeo Tango radar identified at one
two thousand. Request descent on one three five decimal three."
FART: "Alpha Romeo Tango."
*Phew* No more darned position reports. The enroute phase of flight
goes on uneventfully from there. Note that while position reports are no
longer necessary, this does not preclude a pilot from calculating estimates
for the flight plan. They should still be considering Estimated Time Enroute
(ETE) for many reasons, not the least of which is ensuring the fuel remaining
is adequate. Next week, our pilots will be ready for descent.
Well, what do you think so far about our flight? I'm happy to take any
e-mails regarding any phase so far discussed, or items that this example
flight has raised as possibilities for discussion after landing in the coming
weeks. My e-mail address is moxner@nbnet.nb.ca.
Thanks once again for visiting, especially to those who have taken the time
to write in the past week.