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probably ‘reaching’ 5,000, etc. Even our readback to the
controller with ‘leaving’ didn’t catch the different wording.” “Reaching” and “leaving” are commonly used ATC
terms having different usages. They may be used in
clearances involving climbs, descents, turns, or speed
changes. In the cockpit, the words “reaching” and “leaving” sound much alike.
For altitude awareness during climb, professional pilots
often call out altitudes on the flight deck. The pilot
monitoring may call 2,000 and 1,000 feet prior to
reaching an assigned altitude. The callout may be, “two
to go” and “one to go.” Climbing through the transition altitude (QNH), both pilots set their altimeters to
29.92 inches of mercury and announce “2992 inches”
(or ‘standard,’ on some airplanes) and the flight level
passing. For example, “2992 inches” (‘standard’),
flight level one eight zero.” The second officer on three
pilot crews may ensure that both pilots have inserted
the proper altimeter setting. On international flights,
pilots must be prepared to differentiate, if necessary,
between barometric pressure equivalents with inches
of mercury, and millibars or hectopascals, to eliminate any potential for error, for example, 996 millibars
erroneously being set as 2996.
For a typical IFR flight, the majority of inflight time
often is flown in level flight at cruising altitude, from top
of climb to top of descent (TOD). Generally, TOD is
used in airplanes with a flight management system
(FMS), and represents the point at which descent is first
initiated from cruise altitude. FMSs also assist in level
flight by cruising at the most fuel saving speed, providing continuing guidance along the flight plan route,
including great circle direct routes, and continuous evaluation and prediction of fuel consumption along with
changing clearance data. Descent planning is discussed
in more detail in the next chapter, “Arrivals.”
AIRCRAFT SPEED AND ALTITUDE
During the en route descent phase of flight, an additional benefit of flight management systems is that the
FMS provides fuel saving idle thrust descent to your
destination airport. This allows an uninterrupted profile
descent from level cruising altitude to an appropriate minimum IFR altitude (MIA), except where
level flight is required for speed adjustment.
Controllers anticipate and plan that you may level off at
10,000 feet MSL on descent to comply with the Part 91
indicated airspeed limit of 250 knots. Leveling off at
any other time on descent may seriously affect air traffic handling by ATC. It is imperative that you make
every effort to fulfill ATC expected actions on descent
to aid in safely handling and expediting air traffic.
ATC issues speed adjustments if you are being radar
controlled to achieve or maintain required or desired
spacing. They express speed adjustments in terms of
knots based on indicated airspeed in 10 knot increments except that at or above FL 240 speeds may be
expressed in terms of Mach numbers in 0.01 increments. The use of Mach numbers by ATC is restricted
to turbojets. If complying with speed adjustments,
pilots are expected to maintain that speed within plus
or minus 10 knots or 0.02 Mach.
Speed and altitude restrictions in clearances are subject
to misinterpretation, as evidenced in this case where a
corporate flight crew treated instructions in a published
procedure as a clearance. “…We were at FL 310 and
had already programmed the ‘expect-crossing 慬瑩瑵摥
3-23
of 17,000 feet at the VOR. When the altitude alerter
sounded, I advised Center that we were leaving FL 310.
ATC acknowledged with a ‘Roger.’ At FL 270, Center
quizzed us about our descent. I told the controller we
were descending so as to cross the VOR at 17,000 feet.
ATC advised us that we did not have clearance to
descend. What we thought was a clearance was in fact
an ‘expect’ clearance. We are both experienced
pilots…which just means that experience is no substitute for a direct question to Center when you are in
doubt about a clearance. Also, the term ‘Roger’ only
means that ATC received the transmission, not that they
understood the transmission. The AIM indicates that
‘expect’ altitudes are published for planning purposes.
‘Expect’ altitudes are not considered crossing restrictions until verbally issued by ATC.”
HOLDING PROCEDURES
The criteria for holding pattern airspace is developed
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Instrument Procedures Handbook (IPH)仪表程序手册下(71)
