Thanks everyone for chipping in! A thread that runs itself!
Just one thought so far, to add:
Remember that we don't always fly the aircraft through the FMS. There are several ways of actually 'flying' the aircraft, so let's review them, starting with the most basic:
(i) Hand-flown, raw data. Here, the aircraft is flown in the same manner as a Cherokee or Cessna single. The pilot moves the flying controls and throttles, scans the instruments, and adjusts pitch, power, and so on, in order to achieve his desired flight path. Workload is very high, and this is usually reserved for visual approaches or when something has gone very badly wrong!
(ii) Hand-flown, with Flight Director. Here, the pilot flies by hand, but the 'Non-flying Pilot' programmes the Flight Director to give appropriate modes of flight. Workload is lower, accuracy is improved.
(iii) Autopilot, and basic Flight Director modes. Here, the aircraft s flown automatically, and instead of one pilot flying and the other monitoring, both are effectively monitoring most of the time. The 'Flying Pilot' flies the aircraft using modes like Heading Select (HDG SEL) and Level Change (LVL CHG), to achieve the desired profile. Workload is lower, accuracy is better. Almost always, the authothrottle will be engaged too. Regarding modes available, these are some common ones, as Boeing call them. The Airbus ones are similar:
HDG SEL: the aircraft follows the selected heading;
VOR/LOC: the aircraft tracks the selected radial or LLZ course;
LVL CHG: the aircraft climbs with full thrust or descends with idle thrust;
V/S: The aircraft controls speed with thrust and rate of climb or descent with pitch attitude. Can be used in climb or descent, but not commonly employed in climb;
G/S: the aircraft follows the glideslope;
TO/GA: the aircraft climbs at a pre-determined rate of combined climb and acceleration, with go-around thrust, reduced go-around thrust, or take-off thrust as appropriate;
(iv) FMS navigation in lateral and/or vertical sense: The aircraft follows the pre-programmed FMS path in terms of altitude and tracking. Very little pilot intervention is required. The modes are:
LNAV: lateral tracking, following the 'magenta line';
VNAV: vertical profile, following the most economic, or fastest, or longest range, path. this is inluenced by many things including wind data inputs, sensed wind, and input Cost Index (a comparative metric relating to the relative costs of having the aircraft airborne and the cost of fuel).
Don't forget that you can mix and match. We often fly in LNAV, with the aircraft following tracks itself, but in more basic pitch modes than VNAV. Thgis is particularly so when making ATC restrictions or following instructions like 'Descend now'.
Purists will note that I've left out VNAV SPD, as it's efectively the same as LVL CHG, and Control Wheel Steering (CWS), as this is irrelevant to normal line operations on big jets.
Hope this is still of help.
Last edited by NorthernSky; 29th Aug 2002 at 20:30.