Question 16: The answer is C — Page 632, Lesson 731

We're in the answers section now, so I'll walk you through each of these solutions one by one, explaining the reasoning behind each correct answer. Question 16: The answer is C. This is based on radio altimeter height above terrain. Remember, the radio altimeter gives you the actual height above the ground below you, not pressure altitude. That's the key input here. Question 17: The answer is B. The inputs to the Ground Proximity Warning System, GPWS, are: radio altimeter, vertical speed, ILS glide slope deviation, undercarriage position, flap position, and Mach number. So six inputs total. Let me say those again slowly: radio altimeter, vertical speed, ILS glide slope deviation, undercarriage position, flap position, and Mach number. That's the complete list. Question 18: The answer is B. 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 the key idea is that after one failure, the system still works well enough to finish the landing and the roll-out on the runway. Question 19: The answer is C. This is about two different systems. The autopilot synchronization system prevents 'snatching' of the flying controls on engagement of the autopilot. 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 prevents snatching when the autopilot comes on, the other prevents snatching when it comes off. Question 20: The answer is D. Exhaust Gas Temperature, EGT, is measured using a number of thermocouples connected in parallel to minimize the effect of failure of one of them. So if one thermocouple fails, the parallel connection means the others still give you a reading. Question 21: The answer is B. This is 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. There's a diagram here showing the pivot, centre of mass, acceleration, and N for north. Question 22: Answer B. Question 23: Answer C. Question 24: Answer B. Question 25: Answer B. Question 26: The answer is A. A trihedron is defined as a figure having three sides. Additionally, the Inertial Reference System, IRS, establishes true north. Magnetic indications are obtained by the application of variation, which, in the case of the Boeing 737-400, is stored in each IRS memory. The range covered for variation is from 73° North to 60° South latitude. Question 27: The answer is A. Total Air Temperature, TAT, is warmer than Static Air Temperature due to the effect of compressibility. The faster the aeroplane flies, the greater the TAT. So compressibility heating increases with speed. That's the full set of answers for this section.