You've upgraded your airplane from the fixed-gear IFR trainer in which you earned your instrument ticket. Isn't it time you upgraded your instrument flying skills? Instead of using techniques designed for the newly-minted instrument pilot, why not transition to those developed for more experienced pilots flying faster, more capable aircraft? Contributor R. Scott Puddy discusses the benefits and how to make the transition work for you and your airplane.
July 10, 2002
|About the Author ...
R. Scott Puddy was an ATP, CFI, CFI-I, MEI who taught out of the
Buchanan Field Airport (CCR) in Concord, California. Scott was type-rated
in the Beech/Raytheon King Air 300 series but regularly flew a V35 Bonanza
and practices law in San Francisco.
On the morning of June 18, 2002, Scott perished doing what he
loved: practicing aerobatics in a Yak-52, in the mountains of Brentwood,
He contributed many articles about flying to AVweb in recent
years and also worked as our features editor. His enthusiasm for
aviation and his intensity in pursuing it were simply extraordinary.
Even more extraordinary was his dedication to sharing his passion for
flying with others, by teaching and writing. He touched a lot of lives,
undoubtedly saved many, and his legacy of written words will continue
to do both for many years to come. Scott's warmth, wit, and keen
intelligence will be missed by all who knew him and worked with him.
earned your instrument rating several years ago, you have acquired a fair
amount of instrument experience and a corresponding level of comfort in IMC.
You also purchased an assortment of "dot com" stocks 18 months ago
and cashed out before the Federal Reserve raised interest rates for the sixth
time in 12 months. That venerable C-172 treated you well over the years, but
you are flying more long cross-country flights these days. You have the cash,
so you recently upgraded to Airplane 2.0.
Your new plane has an IO-520 up front (or one on each wing). It is fast but
slippery, a nasty trait that is most apparent when you are attempting
straight-and-level in IMC. Controllers used to be much more polite when you
were flying your Skyhawk. You were considering requesting block altitudes for
all IMC flights when you discovered that you could keep the beast more or less
under control if you selected 45% power for cruise. For flights faster than
that, you select "Altitude Hold" on your approach-coupled,
The problem is neither you nor your airplane. When you step up to
high-performance airplanes, you need to upgrade to a high-performance
instrument scan. Here's how.
The FAA Way
The Primary/Supporting Scan
If your instrument instructor adhered to FAA guidance, you initially
trained under the FAA's primary/supporting instrument scan regimen. Under this
technique, the FAA proclaims that all six of the basic flight control
instruments are created equal. Depending on the phase of flight, certain of
those instruments are designated as the "primary" instruments and
are to receive closer scrutiny than the other, supporting instruments. The FAA
acknowledges that the attitude indicator is the only instrument that gives a
direct indication of the airplane's attitude. However, the attitude indicator
is never designated as a primary instrument for any single phase of flight.
Just in case you have not recently reviewed the FAA Instrument Flying
Handbook (AC 61-27C), the FAA designates primary and supporting instruments as
AI = Attitude Indicator
DG = Directional Gyro
ALT = Altimeter
VSI = Vertical Speed Indicator
ASI = Airspeed Indicator
TC = Turn Coordinator
Would The FAA Lead You Astray?
Although this article recommends that experienced instrument pilots use an
alternative scanning technique in high-performance aircraft, the
primary/secondary scanning technique is appropriate for use by instrument
students and inexperienced instrument pilots and is the method to use when the
attitude indicator is inoperable. The FAA counsels all beginning instrument
students (and the instructors who teach them) to de-emphasize use of the
attitude indicator in order to develop the student's instrument scan and for
reasons of safety (in case the pilot may be so unlucky as to experience a
vacuum failure in IMC early in his or her instrument-flying career).
your primary flight training, you were required to receive merely three hours
of instrument training. This included exposure to straight and level flight,
constant airspeed climbs and descents, turns to a heading and recovery from
unusual flight attitudes solely by reference to the airplane's instruments.
Also included were radio communications, the use of navigation systems and
facilities and receiving radar services appropriate to instrument flight.
Those subjects necessarily received limited treatment and the FAA
appropriately refers to this initial instrument work as "emergency flight
by reference to instruments." If you were like most students, you learned
to perform the required maneuvers by fixating on the attitude indicator as
though it were the only instrument on the panel.
Fixating on any one instrument is antithetical to instrument flying, which
requires the development of three fundamental skills: instrument cross-check,
instrument interpretation, and aircraft control. Flight instruments and the
systems that support them fail from time to time. You must cross-check the
instruments against one another in order to detect such a failure and to avoid
unintended and undesirable aerobatic flight in IMC. In addition to calling a
controller's unwanted attention to yourself, these are the kind of maneuvers
from which accident reports are made. Your first task as an instrument
student, therefore, was probably to unlearn the habits developed during your
initial "emergency instrument training."
is much more difficult to unlearn and relearn than it is to start from
scratch. In flight-instructor jargon, the problem is called "negative
transfer" or "interference." The practical implication is that
scanning the flight instruments other than the attitude indicator must be
given disproportionate emphasis during the initial phases of instrument
training in order to overcome the student's established habit of fixating on
the attitude indicator. That is one reason that we use the primary/supporting
instrument scan, which relegates the attitude indicator to a supporting-actor
The second reason for the FAA's primary/supporting instrument scan relates
to the instrument student's post-certification life expectancy. Vacuum pumps
fail about every 1,000 hours or so. Unfortunately, the low-time instrument
pilot does not know whether the next hour in IMC will be the hour.
1,000 newly minted instrument pilots were to launch for an hour's flight in
the clouds, the odds are that one of them would probably end up shooting a
partial-panel approach. Provided that all those pilots were trained in
accordance with the FAA's Instrument Flying Handbook, the pilot who was
singled out by fatigued carbon vanes should do just fine because the failed
attitude indicator was merely a supporting (and not a primary) instrument.
Using the FAA's primary/supporting scan allows the inexperienced or occasional
instrument pilot to use a single scanning technique for both full panel and
Moving Up; Moving On
you are moving up, then it is time to move on. Once you have gotten your wings
wet in IMC, there is no reason to prepare for a once-in-a-thousand-hour
emergency by acting as though the emergency condition constantly exists. The
attitude indicator sits front-and-center in the standard instrument layout for
a reason. Commentary from countless aviation writers to the effect that any
failure of the attitude indicator should be treated as an actual emergency
exists for another good reason. Commercial airliners have at least three
attitude indicators installed for the same reason. The reason is this: The
attitude indicator is the most important instrument on the panel. Ignoring the
attitude indicator because it might someday fail is not quite as bad as
setting your plane on fire to retain currency in forced landings, but ...
well, you get the idea.
Using the primary/supporting scan needlessly forces you to fly your plane
differently in IMC than in VMC. There you go, motoring along on an instrument
flight plan in VMC. You are a well-trained pilot, so you control the airplane
primarily by reference to the visual horizon. Your attention is outside the
plane at least 80 percent of the time and you only occasionally glance at the
directional gyro and the altimeter to confirm that you are holding the
appropriate heading and altitude.
you encounter ... a CLOUD. According to the primary/supporting
method of scanning, you should immediately attempt to control altitude by
focusing primarily on the altimeter and heading by focusing primarily on the
directional gyro, cross-checking the attitude indicator from time-to-time
because it is a supporting instrument for both pitch and bank in
straight-and-level flight. Why should you cross-check the altimeter and
directional gyro only occasionally in VMC and rivet your attention on those
instruments upon encountering IMC?
Attitude Instrument Flying
Yet another and more technical reason for upgrading your technique is that
the primary/supporting scan contravenes the most basic and fundamental concept
of instrument flying. The name of the game you are playing is "Attitude
Instrument Flying." The central rule to the game is:
POWER + ATTITUDE = PERFORMANCE
That formula guarantees you that, if you select an appropriate power
setting and place the airplane in a constant attitude in coordinated flight,
the airplane will give predictable future performance. Your capability to
predict (and hence to anticipate and correct) the airplane's future
performance is the key to operating high-performance aircraft smoothly in IMC.
To enforce that rule, you must be able to hold the plane in a constant
attitude. To maintain a constant attitude you need to focus on the attitude
indicator. The attitude indicator is the only instrument on the panel that
gives instantaneous and direct information about the airplane's pitch and bank
need to use the attitude indicator to establish and maintain an attitude can
be clarified by examining the limitations of the flight instruments. The
information they provide differs greatly from one point in time to the next
based on the degree to which the airplane's attitude is changing. These points
in time are: (1) the past, (2) the present, and (3) the future.
Past, Present And Future...
As discussed above, the pitch control instruments in straight-and-level
The altimeter reacts to changes in barometric pressure and gives
instantaneous information about the airplane's current altitude. The altimeter
reflects the present.
The vertical speed indicator depends upon a "calibrated leak" for
its indications. One result of this design is a distinct lag between a change
in the airplane's attitude and related information appearing on the
instrument. The VSI reflects the past.
Of the "pitch control instruments," the attitude indicator is the
only one that predicts the future. It gives instantaneous and
direct information about the pitch attitude of the airplane. By holding power
and attitude, you can control what the resulting performance will be. Hence,
if in straight-and-level flight the airplane were to pitch to a climb
attitude, the attitude indicator is the only instrument on board that would
allow you to correct for an altitude deviation before the
airplane began a climb or a descent.
As the above discussion suggests, the limitations of the primary/supporting
scan in high-performance airplanes are most evident in controlling altitude.
In a Bonanza for example, if you were to focus on the altimeter as the primary
means of controlling pitch you would constantly be setting off alarms at the
controller's scope as you busted your assigned altitude by 200 feet or more.
This is because a high-performance plane is capable of departing from its
existing altitude quite rapidly. By the time you detect that an altitude
deviation has occurred, the airplane can be off altitude by hundreds of feet.
Moreover, deviations in altitude will distract your attention from the
directional gyro and lead to deviations in heading as well.
you use the altimeter as the primary instrument for pitch in a
high-performance plane, you will constantly find yourself "behind"
the plane. Although the altimeter gives information about the plane's present
performance, there is a time lag associated with your need to cross-check and
interpret it and the other instruments. You will constantly be reacting to
what the plane has already done, or "chasing" the airplane. Your
reaction, if you are like many transitioning pilots, may be to use reduced
power settings in actual or simulated IMC. Unable to keep up with a
high-performance plane using the FAA's primary/supporting scan, you may resort
to reducing power and converting your high-performance airplane to a
low-performance airplane to accommodate the limitations of your technique.
That is not the answer. The answer is to change the way you fly in IMC.
Introducing The Control/Performance Scan
neither the FAA nor your flight instructor told you this, there is another way
the control/performance scan. At first glance, the control/performance scan
appears remarkably similar to the primary/supporting scan. Five of the six
basic flight control instruments are treated exactly the same as before. One
instrument, the attitude indicator, is singled out for special consideration.
Although there are substantial similarities between the two methods, the way
you will fly in IMC using the control scan will be markedly different than
The control/performance scan divides the panel instruments into categories
that give credence to the truism that the airplane's performance is a function
of power and attitude. They are:
In the control/performance scan technique, the instruments that inform the
pilot of the airplane's power setting (usually the manifold pressure gauge)
and attitude (the attitude indicator) are designated as the "Control
Instruments" and are assigned the top tier. Of course, power adjustments
in cruise are relatively infrequent or certainly should be so the
practical effect is that the attitude indicator rests alone atop the heap. You
will make all control inputs with reference to the attitude indicator to
maintain an attitude that will yield the desired indications on the
Performance Instruments reside in the second tier and consist of the other
five familiar gauges. They are assigned "primary" or
"supporting" status for each flight regime in the same manner as
under the primary/supporting scan. The "primary" instruments are the
ones that reflect the value the pilot is attempting to maintain. For example,
in level flight at 7,500 feet, the primary pitch instrument is the altimeter,
since it is the only instrument that shows 7,500 feet. In a 500-fpm
constant-rate climb, the primary pitch instrument is the VSI, as it is the
only instrument that shows 500 fpm. By extension, in a 90-knot constant-rate
climb, the primary pitch instrument is the airspeed indicator because it is
the only instrument that shows 90 knots.
...And Navigation Instruments
the third tier there are the "Navigation Instruments" (e.g., VOR/LOC/GS,
ADF, GPS), but a discussion of this instrument group is beyond the scope of
this article. Of course, if you don't know that these instruments indicate
where the aircraft is and how it can get where it's going, then a quick call
to your CFII to schedule some instruction is probably in order.
In sum, the control/performance concept recognizes that there is a
cause-and-effect relationship between the indications maintained on the
instruments in the higher tiers and the values that will result on the
instruments in the lower tiers. You will use the Control Instruments to
achieve the desired indications on the Performance Instruments. You will
choose target indications on the Performance Instruments that will yield the
desired indications on the Navigation Instruments.
that sounds pretty technical, so let's consider what it means in conjunction
with the most usual flight regime: straight-and-level flight. Here you go
again, motoring along on an instrument flight plan in VMC. You are controlling
the airplane primarily by reference to the visual horizon and only
occasionally glance at the panel to confirm that you are maintaining the
appropriate altitude and heading.
Suddenly, you again encounter ... a CLOUD, but this time you
continue to fly the airplane exactly as before. You merely substitute the
visual cues of the "artificial horizon" for the visual cues of the
visual horizon. You maintain a cruise power setting. You hold the airplane in
a constant attitude by reference to the horizon (attitude indicator). You
periodically cross-check the directional gyro and the turn coordinator on a
supporting basis to confirm that you are maintaining the appropriate
heading. You also cross-check the altimeter and the VSI on a supporting
basis to confirm that you are holding the desired altitude.
upgrade to a more high-tech panel, you will devote even more of your attention
to the attitude indicator. For example, a flight director is a common option
in the general-aviation fleet. The altitude-hold and heading-hold features of
the flight director eliminate the need to cross-check the altimeter and
directional gyro to confirm that you are maintaining altitude and heading.
With all that information available on one instrument, the cross-check serves
simply to assure that the thing is not broken.
Later in the flight, you are still in IMC when the time comes to turn 90
degrees to the left. That will require a transition from one phase of flight
(straight-and-level) to another (standard-rate level turn). The transition
will take only two to three seconds. Just as your attention should be focused
outside the airplane in a transition to a turn in VMC, your attention should
be focused solely on the attitude indicator during the transition in IMC. This
is not the time to be scanning the engine gauges. The attitude indicator is
the only instrument on the panel that gives instantaneous
indications of both pitch and bank. By looking at the attitude indicator while
you roll into a turn, you can assure that you maintain the appropriate pitch
attitude while you change the bank from 0 degrees to the 15 degrees or so
required for a standard-rate turn.
requires discipline to fixate on the attitude indicator during transitions and
you may be surprised how much trouble you have in remembering to focus on a
single instrument during a two-to-three-second time period. Other than lack of
discipline, the problems again are "negative transfer" and
"interference." Having been taught for years to scan all the
instruments on the panel, you may have trouble fixating on one instrument,
even if it is for only two to three seconds.
A failure to use the attitude indicator for transitions is easy enough to
detect: If you depart the assigned altitude while rolling into a turn or leave
an assigned heading while changing pitch, it is a sure sign that you were not
looking at the attitude indicator during the transition.
other bugaboo that frequently arises with transitions to turns is the heading
bug. When assigned a new heading, some instrument pilots have a habit of
adjusting the heading bug to the new heading as they roll the airplane into a
bank to initiate the turn. The heading bug is attached to the directional
gyro. If you are resetting the heading bug, you are looking at the directional
gyro not the attitude indicator. The answer is to reset the
heading bug first, and then to transition into the turn using the attitude
Once established in the turn, you once again control the airplane by
holding it in a constant attitude, primarily by reference to the attitude
indicator. You occasionally cross-check the altimeter and the VSI on a
supporting basis to confirm that you are holding altitude, and cross-check
the turn coordinator to confirm that you are turning at a standard rate.
Fifteen seconds or so into the 90-degree turn, you begin to cross-check the
directional gyro to avoid overshooting your new heading. About eight degrees
(half the angle of bank) before reaching the new heading, you roll to
straight-and-level using the attitude indicator.
...Climbs, Descents And Takeoffs
Executing climbs and descents, and transitions to and from climbs and
descents using the control/performance scan, adds another requirement. In
addition to using the control/performance scanning technique for instrument
cross-check and instrument interpretation, you must also use the correct
inputs for aircraft control. Visible moisture does not negate the fundamental
principles of aerodynamics and you may have become a little lazy over the
years. To fly high-performance airplanes smoothly in IMC, you need to fly
common problem is the failure to maintain coordinated flight. Coordinated
flight is essential to keeping your passengers comfortable and also to assure
that the attitude you hold will yield the performance you desire. The attitude
indicator reflects only pitch and bank; it does not reflect yaw. Therefore,
you could maintain a wings-level (straight) attitude and nevertheless make an
uncoordinated, skidding turn to the left by applying left rudder.
Excessive left rudder is the equivalent of insufficient right rudder. A
high-performance single will likewise yaw to the left if you fail to input
sufficient right rudder pressure when it is required due to the
sometimes-ignored left-turning tendencies: 1) asymmetrical disc loading, 2)
torque, and 3) prop wash. If your high-performance plane has a single IO-520
under the cowl, it has left-turning tendencies in spades in a climb. If you
maintain wings-level in a climb and leave your feet on the floor, your plane
will yaw dramatically to the left. In a climb, to hold a constant heading
using the attitude indicator, you must center the ball with right rudder. In a
descent you need left rudder, but to a lesser extent.
left-turning tendencies are also a factor during low visibility takeoffs. On
the runway, as the airplane attempts to veer into the left hedgerow, you will
receive ample feedback through the right rudder pedal. The airplane will not
turn left unless the nose wheel also turns left. The nose wheel is connected
to the rudder pedal which tells you that the plane is attempting a left turn.
You instinctively counteract with right rudder pressure to hold the airplane
Upon rotation you will lose that feedback when the nose wheel breaks
ground. The tendency therefore is to reduce right rudder pressure upon
rotation. At the same time that the sensation of a need for right rudder
pressure decreases, the actual need for right rudder pressure increases.
The rotation increases the angle of attack and exacerbates the airplane's
left-turning tendencies. In order to maintain coordinated flight (and a
constant heading using a wings-level attitude) you need to increase right
rudder input upon rotation. Otherwise, your high-performance single will turn
(yaw) dramatically to the left.
You now can fly level and perform climbs and descents using the
control/performance scan. But, in order to transition smoothly between those
phases of flight, we need to review yet another aerodynamic principle that you
learned during your primary training: static longitudinal stability.
Certification requirements compel airplane manufacturers to demonstrate
that control forces will vary proportionately with changes in airspeed. As
airspeed increases, you will feel the need for a proportionately greater
"pitch-down" control input in order to maintain level flight. As
airspeed decreases, you will feel the need for a proportionately greater
"pitch-up" control input to maintain altitude. The means by which
manufacturers meet the static longitudinal stability requirement is a lengthy
subject that will have to wait for another article.
Meanwhile, the ramifications of immediate significance to you for flight in
Required pitch inputs will vary proportionately with changes in
Required pitch inputs will continue to change so long as
airspeed is changing.
Static longitudinal stability will present a problem to you when you
upgrade to high-performance planes capable of operating over a greater speed
range than the instrument trainer in which you earned your rating. In an
instrument trainer you might cruise climb at an airspeed of 95-100 KIAS. When
you push the nose down to a level flight attitude at 8,000 feet MSL or so,
indicated airspeed will increase in a short time to 105-110 KIAS, an increase
of about 10 knots or about 10 percent.
In a Bonanza or other Airplane Version 2.0, you will cruise climb at around
105 KIAS and your indicated airspeed at 8,000 will be around 145-150 KIAS, an
increase of 40 knots and about 40 percent. The acceleration will persist for a
longer time in a high-performance airplane and there will be a corresponding
increase in your workload during the transition as the required control forces
could partially circumvent this increased workload by selecting a lower cruise
power setting. That would decrease the airspeed range (and hence the range of
required pitch control inputs). It would also shorten the process of
accelerating from climb speed to cruise speed (because cruise speed will be
lower). Once again, there is a tendency to select lower cruise power settings
in order to convert your high-performance plane to a low-performance plane so
that it will fly more like the aircraft you are accustomed to piloting. Of
course, reducing power for cruise is not the reason you bought Airplane 2.0:
Cruising at a lower power setting could be done just as well and probably
much more cheaply in Airplane 1.0.
Static longitudinal stability is also a factor during transitions from
level flight to a descent. In an instrument trainer, if you push the nose
forward you will experience a modest gain in airspeed and the plane will reach
terminal velocity fairly quickly. If you push the nose over in a Bonanza, you
will gain lots of speed over a prolonged time period. As long as airspeed is
increasing, you will need to increase the "pitch-down" control input
and subsequently "pitch-down" trim to counteract the
airplane's static longitudinal stability. If you neglect to steadily increase
the "pitch-down" control input, the Bonanza will dutifully level off
just as its designers intended.
Once again, you could avoid the need for protracted changes in pitch
control inputs by drastically reducing power in the descent or by lowering the
gear. Most of the time, however, you would prefer to fly gradual descents at
higher speeds. Bonanzas are made to go fast.
Transitions involving deceleration (such as leveling off from a descent at
cruise power) present a similar problem in high-performance planes. A Bonanza
is much more slippery than a C-172 and will consume more time in decelerating
from descent airspeed to cruise airspeed. Throughout the transition, the
required "pitch-up" control force will be increasing.
...And Putting It All Together
Each of the above situations involving protracted changes in airspeed
represents a prolonged transition between phases of flight. Just as you must
fixate on the attitude indicator during the two-to-three seconds that it takes
to transition from straight-and-level to a standard rate turn, you must more
or less fixate on the attitude indicator throughout the one to two minutes
that it takes to transition from climb to cruise, from cruise to descent, or
from descent to cruise.
these transitions, you must fly by sight, not by feel. The moment you take
your eyes off the attitude indicator you will literally lose sight of the
small incremental changes in attitude and will instinctively, by feel, attempt
to hold altitude by maintaining the same control pressures that were
"correct" moments ago. As your airspeed changes, those control
pressures will become incrementally incorrect and you will deviate from your
desired flight path.
The fundamental concept of the control/performance scan is to focus on the
attitude indicator. The requisite near fixation on the attitude indicator
during prolonged transitions is much easier using the control/performance
instrument scan because that is more consistent with the general manner in
which you are flying the airplane.
Other than using the control/performance scan, the two skills that will
help you minimize the increased workload inherent in transitions involving
speed changes in high-performance planes are anticipation and trim. Each of
the above scenarios is a consequence of the fundamental principles of flight.
It is therefore completely predictable, for example, that required
"pitch-down" forces will increase for a minute and a half or so when
you level off to cruise airspeed. That should not catch you by surprise.
Instead, you should plan on it.
As pitch forces increase during a prolonged transition, do not tolerate
them eliminate them with trim. It requires energy to exert force. Moreover,
you cannot fly smoothly using substantial control forces because the muscle
groups capable of generating those forces are not the ones you use for fine
motor movements. Instead, once you have eliminated substantial control
pressures, you can use your fine motor skills to achieve precise attitude
The instrument rating, like any other FAA certificate, is a license to
learn. For good reason, you were initially trained to use the FAA's
primary/supporting scan. However, once you have mastered the fundamental skill
of "instrument cross-check," you should consider upgrading to the
control/performance instrument-scanning technique is for accomplished
instrument pilots. If you are flying or intend to fly high-performance planes
in IMC, it is the technique for you because you need to be an accomplished
instrument pilot to fly powerful, slippery airplanes on instruments. The
technique also works well for accomplished instrument pilots flying
Changing from the FAA primary/supporting scan to the control/performance
scan is not learning something new, it is relearning something old. If the
primary/supporting scan requires you to fly in IMC as though you were partial
panel, the control/performance scan requires you to fly in IMC as though you
were in VMC. The initial feeling is very reminiscent of the first few primary
training flights when you learned to keep your head outside the cockpit and to
control the airplane primarily by reference to the visual horizon. Once you
acclimate to the change, you will fly the airplane more naturally in IMC,
using the same cruise power settings you select in VMC and without having to
request a block altitude.
Whether your are being propelled by an IO-520, a pair of TSIO-360s, or an
O-320, if you switch to the control/performance instrument scan you will also
need to preserve your primary/secondary scanning skills. You will need them to
fly partial panel when not if the attitude indicator or vacuum pump