Brunei DCA CPL(A) Instrumentation common mistakes
Brunei DCA CPL(A) Instrumentation · Understand the traps and how to avoid them.
Treating the static port as the pressure source for the airspeed indicator, so when asked what happens if only the static port blocks, the candidate says the ASI reads zero or fluctuates instead of behaving like an altimeter.
Candidates memorise 'pitot feeds ASI, static feeds altimeter and VSI' as a slogan and forget that the ASI needs both pressures; the static port supplies the reference pressure inside the case.
What to do instead
Draw the ASI case with two inputs: pitot pressure to the capsule, static pressure to the case. With static blocked, the case pressure is trapped at the level where the blockage occurred, so climb gives a decreasing pressure difference and the ASI under-reads, descent makes it over-read. Practise tracing each blockage (pitot, static, drain) through all three instruments until the pattern is automatic.
Confusing the lag/error direction of the altimeter and VSI after a rapid climb or descent, for example claiming the altimeter over-reads after a rapid descent or that the VSI shows an immediate accurate rate.
Candidates learn 'lag' as a word without linking it to the physical cause: the calibrated leak and the capsule's response time mean the VSI lags the actual rate, and the altimeter momentarily misreads while the static pressure equalises.
What to do instead
Learn the mechanism, not the label: the VSI's calibrated leak delays case equalisation, so after a sudden level-off the VSI briefly shows a false climb or descent; the altimeter shows a momentary error in the same transient. Work through one numerical example (e.g. a 500 ft/min climb stopped abruptly) and state which instrument settles first and why.
Applying the magnetic compass turning errors with the wrong sign or the wrong hemisphere, e.g. saying the compass under-reads in a turn from the north in the northern hemisphere, or mixing up acceleration error directions on east/west headings.
The rules (ANDS, UNOS, and the north/south turning dip rule) are memorised as acronyms without a mental picture of the pivot, dip and centre of gravity, so candidates reverse them under exam pressure.
What to do instead
Anchor each rule to the physical picture: in the northern hemisphere the north end of the magnet dips, so in a turn from north it is pulled down and the compass lags (under-reads on northerly headings); acceleration error is greatest on east/west headings because the pivot is tilted fore-and-aft. Re-derive both from the dip picture rather than reciting letters.
Describing the heading indicator as north-seeking and expecting it to correct itself, or failing to state that it must be realigned with the magnetic compass periodically and that it suffers apparent drift due to Earth's rotation.
Candidates lump all gyros together and assume the heading indicator works like a compass, missing that it is a tied gyro with only real drift and apparent drift, and no self-correction.
What to do instead
Contrast the three gyro instruments explicitly: attitude indicator is earth-referenced (erection system), heading indicator is a tied gyro with no erection and drifts, turn coordinator is rate-only. State that apparent drift depends on latitude and that the heading indicator must be reset in level flight against the magnetic compass.
Mixing up the turn coordinator and the turn indicator: claiming the turn coordinator shows rate of turn only, or that it shows angle of bank only, or that the inclinometer is part of the gyro system.
Both use a gyro and a ball, and candidates remember 'turn and slip' without noting that the turn coordinator's gyro is canted so it senses both roll and yaw, giving rate of turn and allowing a rate-one turn to be flown even after bank is established.
What to do instead
State the distinction in one sentence: turn indicator shows rate of turn only (yaw), turn coordinator shows rate of turn and rate of roll (canted gyro), and the ball is a separate inclinometer showing slip/skid, not a gyro output. Then explain why the canted gyro makes the turn coordinator usable for standard-rate turns.
Treating a redline or amber EICAS/ECAM message as a routine caution, or answering that the pilot should silence the master caution and continue without identifying the affected system.
Candidates memorise the colour hierarchy loosely and do not connect the alert level to the required action, so they confuse warning (red, immediate action), caution (amber, awareness) and advisory (white/green, information).
What to do instead
Build a three-row table: colour, aural, master light, required pilot action, and one example (e.g. red engine fire warning versus amber low fuel caution). For each, state the first action: memory items for warnings, then checklist; for cautions, identify the system and consult the checklist.
Answering GPWS/EGPWS questions by describing only the 'too low, gear' mode, or claiming EGPWS removes all nuisance warnings, without knowing the basic modes and the difference between GPWS and EGPWS.
Candidates learn one memorable callout and generalise; they do not know that classic GPWS has limited modes based on radio altitude and that EGPWS adds a terrain database and forward-looking alerts.
What to do instead
List the classic GPWS modes by trigger (excessive descent rate, excessive terrain closure, altitude loss after take-off, unsafe terrain clearance with gear/flap, excessive deviation below glideslope) and note that EGPWS adds GPS/terrain-database look-ahead and peaks mode. Learn that radio-altitude-based modes have a lower limit below which they are inhibited.
Describing TCAS resolution advisories as commands the pilot may ignore if traffic is in sight, or confusing a traffic advisory with a resolution advisory in the response.
Candidates conflate TCAS with basic traffic display and do not learn that an RA is a manoeuvring command with a defined response time, while a TA is information only.
What to do instead
Separate the two: TA is advisory, no manoeuvre; RA is a vertical manoeuvre command that must be followed promptly (typically within about 5 seconds) unless it conflicts with a higher-priority instruction such as a stall warning. Note that RAs are inhibited below a set radio altitude and that the pilot must not manoeuvre contrary to the RA.
Answering flight director/autopilot mode questions by listing mode names without stating what the aircraft actually does, or failing to mention that the flight director can be used with the autopilot disengaged.
Candidates memorise mode names (ALT HOLD, VOR/LOC, GS, VS) as labels and never link each to the control target and the arming/capture sequence, so they cannot answer limitation questions.
What to do instead
For each mode write three things: what it controls (pitch, roll, or both), what it targets (altitude, vertical speed, glideslope, heading), and how it engages (armed then captured). Add the key limitation facts: flight director commands are displayed on the attitude indicator and can be flown manually, and mode reversions or autopilot disconnect behaviour must be recognised.
When an instrument or display fails, jumping straight to a single cause (e.g. 'the ASI is broken') instead of cross-checking against independent sources, and not stating the pilot response sequence for a glass-cockpit display failure.
Candidates answer failure questions by naming the failed instrument rather than describing recognition, confirmation with a second source, and the standby/partial-panel response, so they miss the marks for pilot action.
What to do instead
Use a fixed routine for every failure question: recognise the abnormal indication, cross-check with an independent instrument (standby ASI/altimeter, second display, GPS), identify the affected system, then state the action (revert to standby instruments, select the alternate display format, fly partial panel, land as required). Practise applying this routine to a blocked pitot, a failed AHRS and a blank EFIS screen.