Descending by reference to instruments means controlling an airplane's descent without relying on the outside horizon. The pilot uses pitch, power, and trim to establish the descent, then checks the flight instruments to maintain the desired airspeed, descent rate, and heading.
During a descent, a continuous instrument cross-check is essential. The attitude indicator provides a pitch reference, while the airspeed indicator, vertical speed indicator, altimeter, and heading indicator help the pilot confirm the airplane's actual flight path and detect deviations.
In this lesson, you will practice constant-airspeed descents and constant-rate descents. You will learn how to establish each descent, monitor the instruments, make small corrections, and level off at the selected altitude. These skills build on Straight-and-Level Flight by Reference to Instruments .
Learn to establish, maintain, and level off from a straight descent using pitch, power, and trim. Use a systematic instrument cross-check to maintain the selected airspeed or descent rate, keep a constant heading, and make smooth, accurate corrections.
Set the appropriate descent attitude, adjust power, keep the wings level, and trim the airplane.
Scan the flight instruments to monitor airspeed, descent rate, heading, and altitude. Recognize deviations and make small corrections.
Anticipate the selected altitude, return to straight-and-level flight, and confirm that the descent has stopped.
Understanding an Airplane Descent
In a controlled airplane descent, the aircraft loses altitude while maintaining a stable flight path. During instrument flying, the pilot uses pitch and power to establish the descent and control its performance.
Two measurements are particularly important: the rate of descent and the angle of descent. They describe different aspects of the airplane's flight path.
Rate of Descent
The rate of descent is how quickly the airplane loses altitude. It is measured in feet per minute (fpm) and displayed on the vertical speed indicator (VSI).
At a constant descent rate of 500 fpm, the airplane loses 500 feet of altitude each minute.
Angle of Descent
The descent angle describes the slope of the airplane's downward flight path. Over the ground, it depends on both the rate of descent and groundspeed.
At the same descent rate, a lower groundspeed produces a steeper descent angle over the ground.
The descent angle is not the same as pitch attitude. An airplane can descend with its nose close to the horizon or even slightly above it. Pitch attitude alone does not tell you how quickly the airplane is losing altitude.
How Pitch, Power, and Trim Work Together
Pitch and power both affect airspeed and the rate of descent. The pilot must coordinate them to achieve the desired performance.
Changing pitch affects airspeed and the flight path. Small pitch adjustments help the pilot maintain the selected airspeed or rate of descent.
Reducing power allows the airplane to descend when pitch is adjusted to maintain airspeed. At a constant airspeed, less power generally produces a greater rate of descent.
Once the desired pitch and power are established, trim reduces the control pressure needed to maintain a stable descent.
Instrument Cross-Check During a Descent
During a descent, a systematic instrument cross-check helps the pilot recognize changes in airspeed, vertical speed, altitude, and heading before they become significant deviations.
Use the attitude indicator as a direct pitch and bank reference, then compare the performance instruments to confirm what the airplane is actually doing.
Reading the Flight Instruments
Shows the airplane's pitch and bank. Use it to set and adjust the descent attitude. It does not directly indicate airspeed or descent rate.
Shows whether the airplane is maintaining the selected airspeed. A change in speed may indicate that pitch or power needs adjustment.
Shows the rate of descent in feet per minute. A conventional VSI responds with some delay, so use its trend rather than chasing every small needle movement.
Confirms that altitude is decreasing. Monitor it regularly to remain aware of the selected level-off altitude.
Shows whether the selected heading is maintained. Changes in power or pitch can introduce yaw or bank tendencies that cause an unintended heading change.
A conventional heading indicator can also drift. Check it periodically against the compass under suitable flight conditions.
Helps detect an unintended turn. The inclinometer ball indicates whether the airplane is in coordinated flight. Compare these indications with the AI and HI.
Engine instruments: Include the tachometer or manifold pressure gauge, as applicable, in your scan to confirm the selected power setting. If an indication seems inconsistent, compare it with other reliable instruments before making a correction.
Adapting the Cross-Check to the Descent
A continuous scan does not mean spending the same amount of time on every instrument. The instruments receiving the most attention depend on the maneuver.
The original StudyFlight diagrams below distinguish the primary scan (red) from the supporting scan (yellow). The colored paths show which instruments deserve attention, not a mandatory order of eye movements.
The diagram illustrates the scan used when maintaining a selected vertical speed.
Pitch: VSI, after stabilization.
Power: ASI.
Bank: HI.
Compare this scan with the constant-rate example: the selected target is now indicated airspeed.
Pitch: ASI.
Power: Tachometer or manifold pressure.
Bank: HI.
In either descent, increase your scan rate during entry or after a correction. During transitions, the attitude indicator remains the direct reference while the performance instruments are still responding.
Cross-Check, Interpret, Correct
Scan the instruments and identify changing indications or developing trends.
Compare the indications to determine what the airplane is doing.
Make a small control adjustment, then check whether the indication improves.
Practical Example: Interpreting a Descent
You are flying a constant-airspeed descent at a selected speed of 100 KIAS. The airplane was initially descending at approximately 500 fpm.
During the next cross-check, you observe:
The lower pitch attitude is consistent with the increasing airspeed and greater rate of descent. The heading has remained steady.
Because this is a constant-airspeed descent, the immediate objective is to return to 100 KIAS. Smoothly raise the pitch attitude slightly, then check the ASI again.
The VSI helps confirm how the flight path responds. However, 500 fpm is not necessarily a required rate in this maneuver. Do not chase that value unless a particular descent rate is also required.
Constant-Rate and Constant-Airspeed Descents
The entry into a constant-airspeed descent and a constant-rate descent is similar. The difference comes after the descent is established: which performance indication becomes primary for pitch control and how pitch and power are coordinated.
In each step, Look First identifies the main instrument reference for that phase. Cross-Check identifies the other instruments to monitor. These are priorities within a continuous scan, not instructions to stare at a single instrument.
Choose the descent airspeed, target altitude, and, for a constant-rate descent, the selected vertical speed.
Note your altitude on the ALT and airspeed on the ASI. Confirm the starting heading on the HI, a level attitude on the AI, and near-zero vertical speed on the VSI.
If necessary, reduce power while maintaining level flight until the airplane reaches the selected descent airspeed.
Keep the ALT steady using pitch adjustments referenced to the AI. Watch the ASI decrease toward the selected speed and confirm the power reduction on the engine instruments. Keep the HI steady.
Reduce power further to an approximate descent setting while smoothly lowering the nose to maintain the selected airspeed.
Use the AI to establish the initial descending pitch attitude. Check the ASI frequently to keep the selected speed. The VSI should begin indicating a descent, the ALT should decrease, and the HI should remain steady.
Constant-Airspeed Descent — Step by Step
Keep the selected indicated airspeed throughout the descentAfter the common entry, concentrate on maintaining the selected indicated airspeed. The ASI is primary for pitch performance, while the engine instruments provide the primary power reference. The HI remains primary for heading control.
Watch the ASI as the descent begins. If airspeed rises above the selected value, use the AI to make a small nose-up pitch correction. If airspeed decreases, make a small nose-down correction.
Confirm the new pitch attitude on the AI, then recheck the ASI. Keep the HI steady and monitor the power setting on the tachometer or manifold pressure gauge, as applicable.
Hold the selected airspeed and allow the VSI to settle at the resulting descent rate. The ALT should show a continuing loss of altitude, while the HI remains steady on the selected heading.
If the ASI is correct but the VSI indicates a different descent rate than expected, check the power setting and aircraft configuration before making a correction. Do not change pitch merely to chase a VSI reading while airspeed is correct.
Once the airplane is stabilized, trim to remove sustained control pressure. Watch the AI for any unintended pitch movement during trimming.
Recheck the ASI to confirm that the selected airspeed remains steady. The VSI should settle near its established rate, and the HI should show no heading change.
Maintain the selected airspeed using the ASI and correct small pitch deviations by reference to the AI. Use the HI to detect and correct any heading deviation.
Monitor the VSI to observe the resulting descent rate. Check the ALT regularly to track your progress toward the selected level-off altitude, increasing attention as it approaches.
Constant-Rate Descent — Step by Step
Maintain the selected vertical speed while controlling airspeedStart with the same descent entry. As the vertical speed approaches the selected value, instrument priorities change. Once stabilized, the VSI becomes primary for pitch performance, while the ASI becomes primary for power performance.
Use the approximate pitch and power settings for your airplane. During the initial transition, watch the ASI to prevent an unwanted speed change. Use the AI to establish and maintain the descending attitude.
Check the VSI as it begins showing an increasing descent rate. Confirm that altitude is decreasing on the ALT and that the HI remains steady. Do not chase the VSI while the indication is still developing.
As the VSI approaches the selected descent rate, shift the primary pitch-performance reference from the ASI to the VSI.
If the descent rate becomes too high, make a small nose-up pitch adjustment using the AI. If the descent rate becomes too low, make a small nose-down correction.
Allow the VSI to respond before making another adjustment. Check the ASI for any resulting airspeed change and the HI for heading stability.
Watch the ASI while the VSI remains near the selected descent rate. If airspeed is below the selected value, increase power slightly. If airspeed is above the selected value, reduce power as needed.
Confirm the change on the tachometer or manifold pressure gauge. Then check the VSI. If the vertical speed changes, adjust the pitch attitude using the AI to restore the selected descent rate.
Continue alternating attention between the VSI and ASI until both indications are stable. Keep the HI in the scan.
Once the VSI and ASI are steady at their selected values, trim to relieve sustained control pressure. Monitor the AI while trimming and recheck both performance indications.
During the stabilized descent, use the VSI to identify a change in vertical speed and the ASI to identify an airspeed deviation. Make small, coordinated pitch and power corrections.
Use the HI to maintain heading and the ALT to monitor the remaining altitude before level-off.
Suppose the selected descent rate is 500 fpm down and the selected airspeed is 90 KIAS.
The VSI indicates approximately 500 fpm down, but the ASI shows airspeed gradually decreasing.
Look first at the ASI: it identifies the power-performance deviation. Increase power slightly, confirming the adjustment on the engine instruments.
Cross-check the VSI: if the descent rate changes, use the AI to make a small pitch correction that restores the selected vertical speed. Then confirm that both VSI and ASI indications are moving toward their selected values.
These values are illustrative. Use the appropriate speeds and power settings for your airplane.
Approaching the Target Altitude: Increase attention to the ALT as the selected altitude approaches. Continue checking the ASI and VSI to confirm the airplane's speed and descent rate. The next section explains when to begin the level-off and how instrument priorities change during that transition.
Leveling Off from an Instrument Descent
To level off from a descent, begin the transition before reaching the selected altitude. The amount of anticipation depends on the descent rate, the airplane's response, and the airspeed you want to maintain in level flight.
The level-off technique can be used after either a constant-airspeed or a constant-rate descent. What changes is whether you want to keep the descent airspeed or accelerate to a higher airspeed.
For example, consider an airplane descending at 500 fpm. Two different level-off objectives require different timing.
Begin raising the nose toward the level-flight attitude and increasing power together, approximately 50 feet above the target altitude.
Increase power approximately 100–150 feet before the target altitude while continuing the descent. Begin the pitch transition later, at about 50 feet above the target altitude.
These distances are training examples for a 500 fpm descent, not fixed values. Actual anticipation depends on aircraft performance and pilot technique. The earlier power increase and later pitch transition are separate actions when accelerating to cruise airspeed.
Level-Off at Descent Airspeed — Step by Step
Stop descending while maintaining the selected descent airspeedMonitor the altimeter and the rate of descent. Prepare to begin the pitch and power transition together before reaching the target altitude.
At the lead altitude, smoothly raise the nose toward the level-flight attitude. At the same time, increase power toward the setting required to maintain the selected airspeed in level flight.
Use the altimeter to capture the selected altitude. Confirm that the VSI approaches zero. Make small pitch and power corrections to maintain altitude and airspeed. Trim once the airplane is stable.
Level-Off at Higher Cruise Airspeed — Step by Step
Continue the descent during acceleration, then capture the selected altitudeIncrease power before beginning the level-off pitch change. In the 500 fpm example above, this starts approximately 100–150 feet before reaching the target altitude. The airplane begins to accelerate.
Continue descending as airspeed increases. The nose may tend to rise, so apply gentle forward elevator pressure as needed to maintain the selected descent rate. Monitor the VSI and altimeter. Do not begin the level-off merely because power has increased.
At the later pitch lead point (approximately 50 feet above the target altitude in this example), smoothly raise the nose toward the appropriate level-flight attitude. Use the altimeter to capture the selected altitude while the VSI moves toward zero.
Hold the selected altitude as the airplane finishes accelerating. Adjust power to stabilize at the desired cruise airspeed. Retrim as the airspeed and attitude stabilize.
During the altitude capture, the altimeter becomes primary for pitch. The airspeed indicator provides the primary performance indication for power control.
Use the attitude indicator to make smooth pitch adjustments, monitor the VSI as it approaches zero, and keep the heading steady.
Level-Off Instrument Scan Diagrams
These original diagrams show the instrument scan during leveling off from two different types of descent. In both cases, attention shifts toward capturing the selected altitude.
The level-off is complete when altitude, airspeed, and heading are stable, with approximately zero vertical speed. Trim to relieve any remaining control pressure.
Resume the normal instrument cross-check described in Straight-and-Level Flight by Reference to Instruments .
Instrument Descent Practice and Review Questions
During an instrument descent, reading the instruments is only part of the task. You must also recognize when the airplane is departing from the intended flight condition and decide whether a correction is needed.
The following exercises use a traditional flight instrument panel. Read the situation, compare the indications, and decide what the pilot should do before revealing the explanation.
Practice: Interpret the Instrument Indications
You are flying a constant-rate descent at 95 KIAS, maintaining heading 180°. Your selected descent rate is 500 fpm.
During your cross-check, you notice the following indications.
- VSI
- −800 fpm , stabilized instead of −500 fpm.
- ASI
- Approximately 95 KIAS.
- AI
- Pitch slightly lower than the previously established descent attitude.
- ALT
- Altitude decreasing steadily.
- HI
- Steady at 180°.
Which flight parameter is outside its selected value?
What adjustment should the pilot make, and which instruments should be checked afterward?
Show Explanation
The descent rate is greater than the selected 500 fpm.
The VSI shows −800 fpm, while the attitude indicator shows a lower pitch attitude than previously established.
Make a small pitch-up correction to reduce the rate of descent. Allow the VSI to respond and verify that it approaches the selected rate.
Continue monitoring airspeed. If it changes, coordinate an appropriate power adjustment while maintaining heading.
You are performing a constant-airspeed descent at 90 KIAS, heading 045°. The descent rate has been approximately 450 fpm.
After a small reduction in power, you adjust pitch to maintain 90 KIAS. The instruments now show:
- ASI
- Steady at 90 KIAS.
- VSI
- −450 → −650 fpm , then stabilizing.
- AI
- Slightly lower pitch attitude, with wings level.
- ALT
- Altitude continuing to decrease.
- HI
- Steady at 045°.
Is the airplane still maintaining a constant-airspeed descent?
Should the pilot immediately change pitch to return to 450 fpm?
Show Explanation
Yes. The selected airspeed remains constant.
The additional power reduction has produced a greater rate of descent while the pilot maintained 90 KIAS.
In a constant-airspeed descent, the vertical speed is not necessarily a fixed target. Do not change pitch simply to restore the previous VSI indication.
Continue monitoring altitude and ensure that the new descent profile remains appropriate. If a specific rate is required, coordinate pitch and power to achieve it.
You are leveling off at an assigned altitude of 4,000 feet, heading 270°. You have already begun the transition toward straight-and-level flight.
However, the following indications appear during your cross-check.
- ALT
- 4,010 → 3,995 ft , still decreasing.
- VSI
- Approximately −250 fpm.
- AI
- Pitch still slightly below the required level-flight attitude.
- ASI
- Airspeed increasing slightly.
- HI
- Steady at 270°.
Has the airplane successfully completed the level-off?
Which indications confirm the problem, and what should the pilot do?
Show Explanation
No. The airplane is still descending.
The altimeter has passed below 4,000 feet and continues decreasing. The negative VSI and lower pitch attitude support this conclusion.
Smoothly correct pitch to arrest the descent. Coordinate power as needed to maintain a suitable airspeed.
Regain the assigned altitude smoothly, then establish stable level flight. Confirm that altitude, airspeed, and heading are maintained before trimming.
Review Questions
Test your understanding of instrument descents. Answer each question before opening the explanation.
01 What is the difference between descent rate and descent angle?
Descent rate describes altitude lost per minute, in fpm. Descent angle describes the slope of the flight path. Over the ground, it depends on descent rate and groundspeed.
02 Which instrument is primary for pitch in a stabilized constant-airspeed descent?
The airspeed indicator is the primary performance instrument for pitch. Use the attitude indicator to make pitch corrections.
03 Which instruments are primary for pitch and power in a stabilized constant-rate descent?
The VSI is primary for pitch, while the ASI is primary for power control. Pitch and power must be coordinated to maintain the selected rate and airspeed.
04 Why should the pilot avoid reacting to every small VSI movement?
A conventional VSI responds with some delay. Small or momentary indications do not always require correction. Compare the attitude, altimeter, and VSI trends before adjusting the controls.
05 Why can heading change when power is reduced to enter a descent?
In a propeller-driven airplane, a power change can alter yaw and roll tendencies. Without appropriate control inputs, the airplane may begin turning. Monitor the heading indicator and maintain coordinated flight.
06 When should you begin leveling off from an instrument descent?
Before reaching the selected altitude. The lead distance depends on the descent rate, aircraft response, and desired level-flight airspeed. Accelerating to a higher speed may require an earlier power adjustment.
07 Which instrument becomes primary for pitch during the level-off?
The altimeter becomes primary for pitch performance during altitude capture. The attitude indicator provides direct pitch reference, and the VSI confirms that vertical speed approaches zero.
08 When should you trim the airplane during an instrument descent?
Trim after establishing the desired attitude and stabilizing the descent. Its purpose is to relieve sustained control pressure, not to replace normal elevator control. Retrim after the level-off when the airplane is stable.
