100+ Free SACAA ATPL Instruments Practice Questions

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Sample SACAA ATPL Instruments Practice Questions

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1Which pressures are supplied to an Airspeed Indicator (ASI) capsule and case to measure indicated airspeed?

A.Total (pitot) pressure is supplied inside the capsule, and static pressure is supplied inside the case.

B.Static pressure is supplied inside the capsule, and total (pitot) pressure is supplied inside the case.

C.Dynamic pressure is supplied inside the capsule, and total pressure is supplied inside the case.

D.Ambient static pressure is supplied to both the inside of the capsule and the case.

Explanation: The Airspeed Indicator measures dynamic pressure ($q = P_t - P_s$). Total pressure (pitot) expands the internal capsule while static pressure surrounds the capsule inside the instrument case, producing a expansion proportional to dynamic pressure.

2If the pitot tube becomes completely blocked by ice while its drain hole remains open, what will the Airspeed Indicator (ASI) display during level flight?

A.The ASI will drop to zero because pitot pressure leaks out through the drain hole.

B.The ASI will freeze at its current reading regardless of changes in airspeed.

C.The ASI will act as an altimeter, indicating an increase in airspeed during a climb.

D.The ASI will indicate an overspeed when accelerating at constant altitude.

Explanation: If the pitot entry blocks while the drain hole remains open, remaining pitot pressure inside the line bleeds off through the open drain hole into the static atmosphere, causing the capsule pressure to drop to static pressure and the ASI to read zero.

3If both the pitot inlet and the pitot drain hole become completely frozen and sealed at 10,000 ft, what happens to the ASI reading during a descent to sea level at a constant true airspeed?

A.The ASI will overread (indicate higher speed) in the descent.

B.The ASI will underread (indicate lower speed) in the descent.

C.The ASI reading will remain completely unchanged throughout the descent.

D.The ASI will immediately drop to zero and stay at zero.

Explanation: When the pitot line is trapped, trapped pitot pressure stays constant at the 10,000 ft value. During descent, static pressure inside the instrument case increases, compressing the capsule and causing the ASI to underread (indicate lower airspeed than actual).

4What is the consequence of a blocked static port during a climb in a conventional pitot-static system?

A.The sensitive altimeter freezes at the altitude where the blockage occurred, the VSI reads zero, and the ASI underreads.

B.The sensitive altimeter overreads, the VSI indicates a rapid climb, and the ASI overreads.

C.The sensitive altimeter underreads, the VSI indicates a descent, and the ASI freezes.

D.The sensitive altimeter freezes at the blockage altitude, the VSI reads zero, and the ASI overreads.

Explanation: With a blocked static line: static pressure trapped in the instrument case freezes the altimeter; the VSI pressure differential across the calibrated leak dissipates to zero; and during climb, decreasing pitot pressure inside the ASI capsule against fixed trapped static pressure in the case causes the ASI to underread.

5When an unpressurized aircraft switch to an alternate static source located inside the cockpit, what errors typically affect the flight instruments?

A.Cockpit pressure is usually lower than ambient due to airflow over the fuselage; altimeter reads high, ASI reads high, VSI momentary climb spike.

B.Cockpit pressure is usually higher than ambient; altimeter reads low, ASI reads low, VSI momentary descent spike.

C.Cockpit pressure is equal to ambient; no errors occur on altimeter or ASI, but VSI displays reverse indication.

D.Cockpit pressure is lower than ambient; altimeter reads low, ASI reads low, VSI reads zero.

Explanation: Airflow over the fuselage creates suction inside an unpressurized cabin, making cabin static pressure lower than outside ambient static pressure. Lower static pressure causes the altimeter to overread (indicate higher altitude), the ASI to overread, and the VSI to show a temporary climb spike.

6What is Equivalent Airspeed (EAS) defined as?

A.Calibrated Airspeed (CAS) corrected for compressibility effects.

B.Indicated Airspeed (IAS) corrected for instrument error only.

C.True Airspeed (TAS) corrected for non-standard ISA temperature.

D.Calibrated Airspeed (CAS) corrected for position and density error.

Explanation: Equivalent Airspeed (EAS) is Calibrated Airspeed (CAS) corrected for compressibility effects. At speeds above 200 knots and altitudes above 10,000 ft, compressibility causes CAS to read higher than EAS.

7An aircraft is cruising at Flight Level 350 where ambient temperature is ISA standard (-55 °C). The indicated pressure altitude is 35,000 ft and TAS is 450 knots. What is the local speed of sound ($a$) and corresponding Mach number ($M$)?

A.Speed of sound = 576 knots; Mach number = 0.781

B.Speed of sound = 661 knots; Mach number = 0.681

C.Speed of sound = 590 knots; Mach number = 0.763

D.Speed of sound = 544 knots; Mach number = 0.827

Explanation: Speed of sound formula is $a = 38.945 \sqrt{T_K}$. At FL350 (-55 °C = 218.15 K), $a = 38.945 \times \sqrt{218.15} = 38.945 \times 14.770 = 575.2 \approx 576$ knots. Mach number $M = \text{TAS} / a = 450 / 575.2 = 0.782 \approx 0.781$.

8How does a mechanical Machmeter compute Mach number from pitot-static pressures?

A.By measuring the ratio of dynamic pressure ($P_t - P_s$) to static pressure ($P_s$) using airspeed and altitude capsules coupled via a mechanical lever linkage.

B.By measuring total air temperature and density altitude directly through an electronic wheatstone bridge.

C.By comparing pitot pressure to standard sea-level pressure of 1013.25 hPa.

D.By dividing True Airspeed from the ADC by an internal chronometric timer.

Explanation: Mach number is a function of $\frac{P_t - P_s}{P_s} = \frac{q}{P_s}$. The mechanical Machmeter combines an airspeed capsule ($P_t - P_s$) and an altitude static capsule ($P_s$) through a ratio linkage to continuously compute Mach number without needing temperature input.

9What is the altimeter temperature error rule of thumb, and what is the true altitude when flying at indicated 10,000 ft with altimeter set to 1013.25 hPa when Outside Air Temperature (OAT) is -25 °C (ISA deviation -20 °C)?

A.Rule: 4 ft per 1,000 ft per °C deviation from ISA; True altitude = 9,200 ft.

B.Rule: 4 ft per 1,000 ft per °C deviation from ISA; True altitude = 10,800 ft.

C.Rule: 10 ft per 1,000 ft per °C deviation from ISA; True altitude = 8,000 ft.

D.Rule: 2 ft per 1,000 ft per °C deviation from ISA; True altitude = 9,600 ft.

Explanation: Altimeter temperature correction formula is $\Delta h \approx 4 \text{ ft} \times \text{Indicated Alt (thousands)} \times \Delta T_{\text{ISA}}$. Here ISA at 10,000 ft is $-5 ^\circ\text{C}$. OAT is $-25 ^\circ\text{C}$, so $\Delta T = -20 ^\circ\text{C}$. Correction $= 4 \times 10 \times (-20) = -800 \text{ ft}$. True altitude $= 10,000 - 800 = 9,200 \text{ ft}$ ('From high to low, look out below').

10What altitude is indicated on a sensitive altimeter when the subscale is set to QNH?

A.Height above Mean Sea Level (MSL) when at the aerodrome.

B.Height above the aerodrome elevation (QFE datum).

C.Pressure altitude above the 1013.25 hPa isobaric surface.

D.Density altitude corrected for non-standard temperature.

Explanation: QNH is the altimeter subscale setting that causes the altimeter to read airfield elevation above Mean Sea Level (MSL) when on the ground at that airfield.

About the SACAA ATPL Instruments Exam

The SACAA ATPL Instruments & Electronics examination tests advanced knowledge of flight and engine instrumentation, air data computers, gyroscopic and inertial reference systems (AHRS/RLG/IRS), EFIS/EICAS/ECAM \architecture, AFCS/Autopilot/Flight Director integration, TCAS II, EGPWS, and magnetic compass systems.

Questions

35 scored questions

Time Limit

90 minutes

Passing Score

75%

Exam Fee

R450 per subject sitting under SACAA Part 187 user fees (South African Civil Aviation Authority (SACAA))

SACAA ATPL Instruments Exam Content Outline

20%

Pitot-Static Systems and Air Data Computers

ASI, Altimeter, VSI, Machmeter, Air Data Computer (ADC/DADC), total air temperature probes, pressure and density altitude calculations, static and pitot blockages.

20%

Gyroscopic Flight Instruments and AHRS

Rigidity in space, precession, Artificial Horizon, Directional Gyro, Turn Coordinator, Ring Laser Gyro (RLG), Fiber Optic Gyro (FOG), AHRS, and Inertial Reference Systems (IRS).

20%

Glass Cockpit Displays and Avionics (EFIS/EICAS/ECAM)

Primary Flight Display (PFD), Navigation Display (ND), EICAS, ECAM, Head-Up Display (HUD), symbol generators, color coding standards, and system redundancy.

15%

Automatic Flight Control Systems (AFCS) & Flight Director

Flight Mode Annunciator (FMA), Autothrottle, lateral and vertical guidance modes, Autoland CAT I/II/III operations, fail-passive and fail-operational \architectures.

15%

Traffic and Terrain Avoidance Systems (TCAS/EGPWS)

TCAS II / ACAS II Traffic Advisories (TA) and Resolution Advisories (RA), EGPWS/TAWS warning modes 1–6, predictive terrain alerting, Radio Altimeter integration.

10%

Aircraft Magnetism and Compass Systems

Direct-reading magnetic compass construction, turning and acceleration errors, hard/soft iron magnetism, fluxgate/flux valve sensors, and remote-indicating gyro-magnetic compasses.

How to Pass the SACAA ATPL Instruments Exam

What You Need to Know

Passing score: 75%
Exam length: 35 questions
Time limit: 90 minutes
Exam fee: R450 per subject sitting under SACAA Part 187 user fees

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

SACAA ATPL Instruments Study Tips from Top Performers

1Master pitot-static failure modes: know the precise instrument indications for pitot blockage (ASI acts as altimeter), static blockage (ASI reads low in climb/high in descent, Altimeter freezes, VSI drops to zero), and alternate static source effects.

2Memorize glass cockpit color coding standards: RED for warnings/immediate action, AMBER for cautions/immediate awareness, CYAN/BLUE for advisory/status, GREEN for engaged modes/normal parameters, and WHITE for \armed modes/scales.

3Understand TCAS II / ACAS II logic: TAs give traffic awareness (35–48 seconds to CPA), RAs provide mandatory vertical maneuvering advice (20–35 seconds to CPA); TCAS II never provides lateral turn commands.

4Practice Mach number and local speed of sound calculations using $a = 38.945 \\sqrt{T_K}$ and $M = \ ext{TAS} / a$, as well as altimeter temperature correction factors (4 ft per 1000 ft per °C deviation from ISA).

5Study modern ring laser gyros (RLG) and AHRS/IRS principles: understand the Sagnac effect, Schuler tuning (84.4 min period), alignment requirements, and fluxgate/flux-valve slaving mechanisms.

Frequently Asked Questions

What is the pass mark and question count for SACAA ATPL Instruments?

Under SACAA CAR 61.01.10, the pass mark is 75%. The computer-based PEXO examination comprises 35 multiple-choice questions with a time limit of 90 minutes.

How much is the examination fee for SACAA ATPL subjects?

The examination fee is R450 per subject sitting under the SACAA Part 187 user fee schedule (approved examination centres may charge an additional facility fee).

What \are the primary calculation topics tested in ATPL Instruments?

Candidates \are tested on altimetry corrections (temperature and barometric error), local speed of sound ($a = 38.945 \\sqrt{T_K}$), Mach number ($M = \ ext{TAS}/a$), density altitude, total air temperature (TAT/SAT recovery factor), and rate-of-turn bank angle calculations.

How do TCAS II Resolution Advisories (RA) affect ATC clearances under SACAA regulations?

Pilot response to a TCAS II RA takes precedence over any conflicting ATC clearance. Pilots must follow the RA immediately, notify ATC as soon as practical, and return to the cleared altitude once the prompt 'CLEAR OF CONFLICT' is issued.

What is the difference between fail-passive and fail-operational autoland systems?

A fail-passive autoland system causes no significant out-of-trim condition upon a single component failure, but requires the pilot to take control; a fail-operational system uses redundant channels to complete the automatic landing without pilot intervention following a single fault.

100+ Free SACAA ATPL Instruments Practice Questions

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