Answer C — Page 632, Lesson 732

Right, let's pick this up. We're looking at the answers to a batch of questions, and I want to walk you through the reasoning behind each one, because these are the kind of concepts that will come back again and again. Let's start with question 28, where the answer is C. This is a nice one for clearing up terminology. We have three terms here. First, isoclinal lines — these refer to magnetic dip. That's the angle between the Earth's magnetic field lines and the horizontal plane. Then we have isobars, which are lines of equal atmospheric pressure on a meteorological chart. And finally, a deviation card — that's a compass correction card positioned alongside the compass in the aircraft. It's the card that tells you the compass error for different headings, so you can correct what you read on the compass. Moving on to question 29, answer A. This is about temperature and altitude. If the actual temperature of the column of air in which the aircraft is flying is COLDER than ISA — that's the International Standard Atmosphere — then the True Altitude of the aircraft above mean sea level will be LOWER than the Indicated Altitude. Conversely, if the actual temperature is WARMER than ISA, the True Altitude will be higher. So the key relationship here is: cold air makes the altimeter over-read, warm air makes it under-read. Question 30, answer A. The air driven artificial horizon is also known as the 'classic attitude indicator'. That's just a naming point — the classic attitude indicator is the one driven by air, as opposed to an electrically driven one. Question 31, answer A. Angular momentum means speed of rotation (rpm). That's the definition we're working with here — the faster something spins, the greater its angular momentum. Question 32, answer A. The error detector is also known as a signal selsyn. A selsyn is a type of synchro system used to transmit angular position, and the error detector is the component that senses the difference between the commanded and actual position. Now, question 34, answer C. This question refers to a ring laser gyro. That's the key subject — a ring laser gyro is a type of gyroscope that uses laser beams to measure rotation, and it's a fundamental instrument in modern navigation. Let's jump ahead to question 42, answer A. This is about gyroscope freedom. The vertical axis means the horizontal plane. The two are at 90° to each other. It follows, therefore, that heading information only requires one degree of freedom in the horizontal plane about the vertical axis of the gyroscope. So for heading, we only need the gyro to be free to rotate about one axis — the vertical one. Question 45, answer D. Here we have a formula for LSS, which stands for Local Speed of Sound. The formula is LSS = 38.94 × √temp in K. That's 38.94 times the square root of the temperature in Kelvin. Alternatively, you can use the CRP 5 — that's the navigation computer, a manual flight computer. And question 46, answer D. This is where we apply that formula. The first thing to remember is that the local speed of sound is dependent on AMBIENT temperature, not ISA. In this case, applying the temperature deviation to the ISA temperature at mean sea level gives an ambient temperature of +5°C. There are two methods of calculating the local speed of sound. The first is to use the formula from question 45. So we take LSS = 38.94 × √278 K. That gives us LSS = 649.26 kt. The second method is to use the CRP 5 navigation computer, which does the same calculation mechanically. So there we have it — a run through of the reasoning behind these answers. Each one reinforces a core principle, whether it's terminology, temperature effects, or the mathematics of sound speed.