Instrument scan and cross-check

Look, interpret, control, and look again

A cross-check is a continuous, logical comparison of instruments for attitude and performance information. Moving your eyes is only the first part. You must interpret the indications together, decide whether they match the intended flight condition, apply a suitable control input, and check its effect.

Ask three questions: What am I trying to maintain or change? What are the instruments actually showing? What small correction will close the difference? In level flight, a near-level attitude indication does not prove that altitude is constant. The altimeter and vertical-speed trend show whether that attitude is producing level flight at the current airspeed and power.

For example, a slow altitude loss together with a nose-low indication suggests a pitch correction. An altitude loss with an unexpected bank also requires attention to bank. Reacting only to the altitude number can hide the reason for the loss. The same process applies to analog instruments and electronic displays.

IFH 6-10–6-13: fundamental skills, cross-check and interpretation · IFH 6-24–6-28: electronic-display cross-check

Let the maneuver determine your attention

The FAA describes several scan patterns. A selected radial scan repeatedly returns to a reliable attitude indicator between checks of other pertinent instruments. An inverted-V or rectangular pattern can help introduce instrument locations. These patterns are learning tools. The useful pattern is the one that repeatedly brings you the information needed for the maneuver.

During a transition, emphasize the attitude and power change while watching the developing performance. Once stabilized, emphasize the indications that verify the assigned altitude, heading, airspeed, or turn rate. Near a level-off or rollout, increase attention to the approaching target without dropping the rest of the cross-check.

A changing heading during a commanded turn is expected; an unplanned altitude loss is not. Studying each maneuver’s expected indications makes the scan selective without becoming narrow. Do not adopt a fixed number of seconds or a fixed percentage of attention as a guarantee of adequate coverage. Return often enough to detect and correct the actual trends.

IFH 6-10–6-13: scan patterns and errors · IFH 6-24–6-28: adapting the electronic-display scan · ACS IV.A, printed page 10

Read direction and rate as well as the number

An instrument’s value tells you where the airplane is now; its trend helps you decide where it is going. An altimeter reading of 4,000 feet with a steady descent is a different situation from 4,000 feet with no altitude change. The first needs a timely response even though the selected altitude has just been reached.

The attitude indicator gives direct pitch and bank information when it is functioning correctly. Altitude, airspeed, and vertical speed show the resulting performance. A conventional VSI has lag: immediately after a pitch change, its indication may still reflect the previous condition or be settling. The airplane itself also takes time to accelerate or decelerate. Continue comparing indications instead of repeating a correction because one indication has not caught up.

Electronic trend vectors can help anticipate altitude, airspeed, or heading. Their prediction time, availability, and symbols depend on the installed system. A vector extends the current trend; it does not promise the future flightpath. Verify the display’s manual, include the underlying value, and cross-check actual attitude and power. A very precise digital number does not justify constant control movements to chase its last digit.

IFH 6-5–6-7: VSI and airspeed interpretation and limitations · IFH 6-26–6-28: trend indicators and fixation

Recognize three different scan errors

Many control problems begin as information problems. Identify the scan error before simply trying to move your eyes faster.

Fixation can come from uncertainty: you may be trying to decode a display or wondering why a number is wrong. Omission can follow an unanticipated transition, such as forgetting airspeed after changing power. Misplaced emphasis can grow from relying on the most familiar instrument even when it cannot answer the present question by itself.

When you catch one of these errors, restore aircraft control and the full cross-check, then simplify the competing task. Discuss recurring errors with your instructor. A smoother scan comes from knowing what each indication means and expecting the next change, not from a speed contest with your eyes.

IFH 6-11–6-13: fixation, omission and emphasis · IFH 6-27–6-28: electronic-display scan errors

When indications disagree, compare sources

A normal maneuver should produce a coherent group of indications. In a stabilized straight climb, altitude should increase, airspeed should settle near the selected climb speed, and heading should remain near the intended heading. A heading change or falling airspeed calls for interpretation and correction. A failure flag or an attitude display that disagrees with the other evidence also calls for a reliability check.

Maintain control using the reliable information while assessing the disagreement. Include standby instruments, system warnings, and power-source indications as appropriate to the aircraft. Two displays fed by the same attitude sensor are two presentations of one source. Airspeed, altimeter, and VSI may share a static source; their agreement does not rule out a common static-system problem.

Do not vote by screen count or assume that the familiar instrument is always right. Know the system’s dependencies before flight, and use the AFM/POH and installed-equipment procedures when a failure is suspected. Avoid making a large control input merely to satisfy one disputed indication. Detailed failure diagnosis and partial-panel control are developed later; this lesson establishes the habit of seeking corroborating evidence without abandoning control.

IFH 11-7–11-8: instrument and system failure recognition · IFH 6-24–6-28: standby information and cross-check

Protect the scan from sensations and distractions

Fatigue, illness, stress, hypoxia, and increasing workload can slow interpretation or narrow attention. Before flight, assess fitness and the demands of the planned trip. During flight, recognize when a radio call, chart search, or avionics entry is taking too much of the attention needed to control the airplane. Organize materials and make longer entries before a demanding transition when possible.

Use short task segments: check the airplane, make a manageable entry, and return to the cross-check. Defer a nonessential task, ask ATC for time or clarification, or use an appropriate trained resource when necessary. An unfamiliar display can add workload even though it presents more information. Before using it in IMC, locate attitude, airspeed, altitude, heading, power, coordination, failure flags, and standby references with your instructor.

Bodily sensations are not an independent instrument. A slow unnoticed bank followed by a correction can produce the leans. Abrupt head movement during a prolonged turn can create a Coriolis illusion. A sloping cloud edge or scattered lights may suggest a false horizon. Use reliable, corroborated instrument references when the visual horizon or sensations are misleading, and avoid sudden extreme head movements. Keep the aircraft control task ahead of the urge to make the sensation disappear.

AIM 8-1-1 through 8-1-3: fitness, hypoxia and stress-related impairment · IFH Chapter 3, 3-4–3-8: sensory systems and disorientation · AIM 8-1-5: illusions in flight · ACS IV.A, printed page 10

Work a drift before it becomes a larger deviation

Training example: the assigned targets are 4,000 feet, heading 090°, and 110 KIAS. These are invented study targets, not aircraft performance data. You briefly look down to change a frequency. On returning, the altimeter shows 3,960 feet and decreasing, heading is moving left through 087°, airspeed is slightly increasing, and the reliable attitude indicator shows a small left bank with a slightly lower pitch.

1. Interpret the group: the airplane is drifting left and descending. The decreasing altitude is a trend, not just a 40-foot error. The attitude and performance indications agree.
2. Restore control: use an appropriate small, coordinated bank correction to stop the unintended turn and a suitable pitch correction to arrest the descent. Verify power and airspeed rather than assuming they are unchanged.
3. Recheck: confirm the heading trend has stopped, then make any small correction toward the assigned heading. Verify the descent arrests and return to altitude smoothly. Trim off sustained pressure after establishing the desired condition.
4. Address the cause: divide future frequency or navigator work into shorter segments. If the task still exceeds your capacity, request time or assistance.

Your instructor will help choose the actual correction size and control sequence for the airplane. The ground exercise prepares interpretation and correction planning under ACS IV.A.S2; it cannot demonstrate the flying skill.

IFH 6-4–6-10: control, trim and cross-check · ACS IV.A, printed page 10

FLIGHT SCENARIO

What would change your plan?