These cover several important topics, so let's take them one by one — Page 160, Lesson 145

I want to walk you through a set of answers from the instruments question bank. These cover several important topics, so let's take them one by one. Starting with question 10: to calculate the rate of descent of an aircraft in feet per minute, the rule of thumb is: 5 × aircraft ground speed. So if your ground speed is 100 knots, 5 × 100 gives you 500 feet per minute rate of descent. That's a quick mental calculation you can use in the cockpit. Question 11 deals with TCAS — Traffic Alert and Collision Avoidance System. There are different versions. TCAS I will issue a Traffic Advisory only, and manoeuvre of the aircraft is prohibited — you don't turn or climb based on a TCAS I advisory, you just look. TCAS II will issue a Corrective Resolution Advisory instructing the pilot to take corrective action in the vertical plane only — that means climb or descend, but no horizontal guidance. TCAS III will issue a Corrective Resolution Advisory instructing the pilot to take corrective action in the vertical and/or horizontal planes — so you could get a turn instruction as well. Now, don't confuse a "Corrective Resolution Advisory" with a "Preventative Resolution Advisory." A Preventative Resolution Advisory only provides limitations on aircraft manoeuvres — it tells you what not to do, like "do not climb." A Corrective Resolution Advisory, by contrast, issues corrective aircraft manoeuvres — it tells you what to do, like "climb, climb." Question 12: a leak in the total pressure line — that's the pitot pressure line — will exhaust a percentage of that pressure to atmosphere. This causes both the ASI, the Airspeed Indicator, and the Machmeter to under-read. The loss of pressure causes the airspeed capsules in both instruments to under-expand. So if you have a pitot leak, your indicated airspeed and Mach number will both be lower than they should be. Question 13: a classic attitude indicator refers to an air-driven artificial horizon — the kind powered by vacuum or pressure, not electric. During a standard 360° turn, certain indications will be apparent. Let me walk through the table. At roll-in, which is the start of the turn, pitch indication is normal and roll indication is normal. At 90° into the turn, pitch reads high — nose up — and roll reads too low. At 180°, pitch reads high — nose up — and roll is normal. At 270°, pitch reads high — nose up — and roll reads too high. At roll-out, back to straight and level, pitch is normal and roll is normal. This error is corrected by the application of compensation tilt, which is a mechanical feature inside the instrument. Question 14 refers back to the answer for question 6, so we'll move on. Question 15: this can be proved on the navigation computer. Set all parameters for ISA — International Standard Atmosphere — at mean sea level. Read off CAS, Calibrated Airspeed, on the inner scale against TAS, True Airspeed, on the outer scale. They are the same. At ISA mean sea level, with no pressure or temperature errors, CAS equals TAS. Question 16: this is based on radio altimeter height above terrain. So whatever the question was, the answer involves the radio altimeter measuring your actual height above the ground. Question 17: the inputs to GPWS — Ground Proximity Warning System — are as follows: i. radio altimeter, ii. vertical speed, iii. ILS glideslope deviation, iv. undercarriage position — that's landing gear position, v. flap position, and vi. Mach number. So GPWS uses all these parameters to determine if you're in a dangerous situation near the ground. Question 18: a system that can withstand at least one failure but leaves the system capable of completing the landing and roll is described as 'fail-operational'. An alternative term is 'fail-active'. So if one component fails, the system still works well enough to finish the landing and the rollout on the runway. Question 19: the autopilot synchronization system prevents 'snatching' of the flying controls on engagement of the autopilot. Snatching means a sudden, jerky movement. The auto-trim system adjusts the trim of the aircraft during automatic flight to prevent 'snatching' of the controls on disengagement of the autopilot. So one system smooths the engagement, the other smooths the disengagement. Question 20: EGT — Exhaust Gas Temperature — is measured using a number of thermocouples connected in parallel to minimize the effect of failure of one of them. If one thermocouple fails, the others still give a reading because they're wired in parallel. Question 21: Newton's third law — to every action there is an equal and opposite reaction. In this case, the forces cancel out and the compass will continue to indicate north. The diagram shows acceleration, a pivot, and the centre of mass. So under certain acceleration conditions, the compass remains steady pointing north because the forces balance.