In order to achieve maximum fuel economy and to prolong engine life, advanced aircraft turbine engines utilise electronic engine control systems. Full-authority electronic engine control systems receive data from the air- craft and engine systems to enable safe and efficient operation of the thrust
management system over the entire operating range of the engines. One aspect of such a system is computation of the optimum and maximum thrust requirement for every condition of flight. The computed total air tempera- ture (TAT) and measured pressure altitude are used to compute the opti- mum and limiting engine pressure ratio (EPR) for the current flight phase. EPR is the ratio of HP turbine exhaust pressure to LP compressor inlet pressure and has been found to be directly proportional to the thrust delivered by the engine.
The computed EPR for the current flight phase is presented on an indi- cator on the flight deck, which typically displays TAT, the current flight mode (e.g. take-off, climb, cruise, etc.) and the EPR limit for that mode. The actual EPR, with limit and target markers, continues to be indicated on the engine monitoring display (e.g. EICAS). Examples of EPR indicators are shown in Figure 5.17.
The flight mode for which EPR computation is required is selected by the pilot through an EPR limit control panel and this is fed to the EPR computer. Typical modes for EPR limit computation are climb (CLB), economy (CON), cruise (CRZ), top-of-descent (TOD) and go-around (GA). When the auto- matic flight control system is in use, go-around EPR limit will automatically display as the glideslope is captured. Additionally, the panel may contain thrust rating selector switches, with which the pilot can command the computer to calculate the EPR for specific engine performance ratings. The system incorporates a test function for preflight testing. In the event of system failure or electrical power loss, a warning flag obscures the EPR limit indicator.
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TAT MODE EPR C O 0.8 1.0 1.2 1.4 1.6 1.8 EPR actual EPR EPR limit reference indicatorSample questions
1. The display screen of a flight management system multi-purpose control and display unit:
a. Provides an analogue display of flight progress? b. Provides an alpha-numeric display of flight plan data?
c. Is divided into two fields, the left field providing information in alpha-numeric form and the right field providing the same infor- mation in analogue form?
d. Provides 24 lines of information, 14 characters per line?
2. The background tape of a flight director ADI normally has . . . . freedom of movement in roll and . . . freedom of movement in pitch:
a. 3608 +908?
b. +908 3608?
c. 908 908?
d. 3608 3608?
3. The aircraft symbol on a flight director HSI: a. Rotates with the compass rose?
b. Aligns with the selected VOR radial? c. Aligns with the selected heading? d. Is fixed at the centre of the display?
4. With VOR selected and the HSI lateral deviation bar displaced one dot to the right, the aircraft is approximately . . . from the radial: a. 58? b. 5 nm? c. 11 48? d. 21 28?
5. The warning flags on a flight director ADI will indicate failure of (answer a, b, c or d):
1. glideslope receiver 2. FD vertical gyro 3. FD computer 4. MHRS signal
5. VOR or localiser signal a. 1, 2, 3, 4, 5?
c. 1, 2, 3? d. 3, 4, 5?
6. With the flight director in VOR/NAV mode, the ADI command bars provide:
a. Guidance in pitch only? b. Guidance in pitch and roll?
c. No guidance, since they are retracted in this mode? d. Guidance in roll only?
7. A two-axis autopilot has:
a. A single inner loop and two outer loops? b. Two inner loops and two outer loops? c. Two inner loops?
d. One inner loop?
8. The data supplied to an autopilot system from the central air data computer are known as:
a. Manual data? b. Manometric data? c. Monometric data? d. Aerodynamic data?
9. The function of a torque limiter in the servo-drive of a flying control surface is to:
a. Prevent excess rate of movement of the surface? b. Prevent slip in the drive system?
c. Control the rate of movement of the surface? d. Prevent over-torquing of the servo-motor? 10. Control wheel steering (CWS) is engaged by:
a. Rotating a knob on the AFDS control panel?
b. Applying normal manoeuvring force to the pilot's controls? c. Operating a thumb switch on the control wheel?
d. Moving the autopilot engage paddles to OFF?
11. With the automatic flight director system in VNAV and LNAV mode, engaging a second autopilot will:
a. Improve the sensitivity of the automatic flight system? b. Automatically engage the autothrottle system?
c. Disengage the active autopilot?
d. Automatically change the control mode to approach mode?
12. LVL CHG, V/S and VNAV modes are inhibited when . . . is engaged:
a. HDG SEL? b. LNAV? c. N1?
d. ALT HOLD?
13. A fail operational automatic landing system:
a. Requires two independent autopilots and one monitoring system? b. Is one which will not continue with an automatic landing in the event
of a single failure within the system?
c. Will abort the landing if a failure occurs below alert height?
d. Requires at least three independent autopilots and two independent monitoring systems?
14. For an automatic landing to continue below 1500 ft, which of the fol- lowing conditions must be satisfied (answer a, b, c or d):
1. Glideslope capture 2. Localiser capture
3. Radio altimeter serviceable 4. Off-line autopilots engaged 5. FLARE mode armed a. 1, 2, 3, 4?
b. 1, 2, 4, 5? c. 1, 2, 3, 4, 5? d. 1, 2, 4?
15. Autothrottle take-off mode is engaged by:
a. A push button switch on the AFDS mode control panel? b. Press switches on the thrust levers?
c. A lever switch on the AFDS mode control panel? d. A push button switch on the control yoke?
16. The factors necessary for computation of EPR limit are: a. TAT, pressure altitude, flight mode?
b. TAT, pressure altitude? c. N1, TAT?