A system utilizing a two-circuit vacuum switch to monitor suction in the fuel system between the fuel selector valve and the engine-driven pump and warn the pilot of a restriction in the system or that the fuel tank from which the engine is feeding is exhausted of fuel.

An integrated aircraft longitudinal flight control system uses a generalized thrust and elevator command computation (38), which accepts flight path angle, longitudinal acceleration command signals, along with associated feedback signals, to form energy rate error (20) and energy rate distribution error (18) signals. The engine thrust command is developed (22) as a function of the energy rate distribution error and the elevator position command is developed (26) as a function of the energy distribution error. For any vertical flight path and speed mode the outerloop errors are normalized (30, 34) to produce flight path angle and longitudinal acceleration commands. The system provides decoupled flight path and speed control for all control modes previously provided by the longitudinal autopilot, autothrottle and flight management systems.

There is proposed a method of controlling an engine aerodyne in the climb phase, wherein a velocity variation law as a function of altitude is imposed. Moreover, there is set a law of variation of the engine speed corresponding generally to progerssive decrease in such speed as altitude increases. Optimization of exploitation costs in the climb phase can be reached mainly by taking into account the engine maintenance costs by means of a wear model.

A fuel time indicator which is removably mountable about a fuel tank selector switch for monitoring and displaying tank usage times for each of a plurality of fuel tanks is disclosed. The fuel time indicator comprises a portable frame including a switch position sensor for monitoring a plurality of positions of the fuel selector switch and generating a corresponding switch position signal. A timer generates a timing signal indicative of elapsed time. A controller responsive to the position signal and the timing signal generates tank usage times for each of the fuel tanks by selectively aggregating elapsed times. Visual indications of the tank usage times are provided by a display.

An avionic system for producing the most economical engine thrust and airspeed settings in readily usable form during a jet aircraft flight is disclosed. The pilot inserts: the elevation of the destination airport; the zero fuel weight of the aircraft; the reserve fuel needed for the flight; the outside air temperature at the departure airport; and, a flight index number. The flight index number represents a chosen relationship between fuel costs and trip time-related costs. The system also receives data from various aircraft subsystems and sensors and uses the information it receives, and stored information, to produce signals representing the most economical engine thrust setting and airspeed for the phases of a flight. The thrust setting and airspeed signals drive bugs on thrust and airspeed indicators and/or used to control autothrottle/autopilot systems. The throttles and pitch attitude of the aircraft are controlled so that the indicator readings "track" the bug positions to cause the aircraft to follow the most economical flight path based on the chosen flight index number. Engine thrust limits are prevented from being exceeded by comparing calculated thrust values with stored engine thrust limit settings; and, using the maximum values to control the position of the thrust indicator bugs and the digital display. Still further, the system develops an aircraft idiosyncrasy factor (K) that is used to modify calculated thrust values in order to compensate for the drag and thrust peculiarities of the aircraft, zero fuel weight errors, etc.