depression definition. A period of drastic decline in the national economy, characterized by decreasing business activity, falling prices, and unemployment. The best known of such periods is the Great Depression, which occurred in the 1930s.
A variometer â also known as a rate of climb and descent indicator (RCDI), rate-of-climb indicator, vertical speed indicator (VSI), or vertical velocity indicator (VVI) â is one of the flight instruments in an aircraft used to inform the pilot of the rate of descent or climb.
Mach number (Ma or M) is the speed of an object moving in air, divided by the speed of sound at that particular conditions, including temperature and pressure. At Standard Sea Level and temperature 15 degrees Celsius, the speed of sound is 761.2 miles per hour (mph) = 340.3 meters per second (m/s) = 1225 km/h = 1116 foot per second (ft/s) = 661.5 knots (kn, kt or kts).