Factual Information 2015:Appendix 1.6E/1.6E.2
This page contains an extract from MH370/01/15 Factual Information which accompanied the (first) Interim Statement released by The Malaysian ICAO Annex 13 Safety Investigation Team for MH370 on 8th March 2015.
1.6E.2 Autopilot Flight Director System (AFDS)
The autopilot is engaged by operation of either of two A/P pushbutton switches on the Mode Control Panel (MCP) located on the glareshield panel (Figure 1.6EA). Once engaged the autopilot can control the aircraft in various modes selected on the MCP. Normal autopilot disengagement is through either control wheel autopilot disengage switch. The autopilot can disengage if the flight crew override an autopilot command through the use of the rudder pedals or control column. The autopilot can also be disengaged by pushing on the A/P Disengage Bar on the MCP. The AFDS consists of three autopilot flight director computers and the MCP.
1.6E.2.1 Roll Modes
The following AFDS roll modes are available during climb, cruise and descent (Figure 1.6EB below):
- a) Lateral Navigation (LNAV)
Pushing the LNAV switch arms, selects or disarms the LNAV mode. The commands come from the active Flight Management Computing Function (FMCF) when there is a valid navigation data base and an active flight plan. The Control Display Units (CDUs) can send LNAV steering commands when there is no active FMCF. The AFDS use this priority to select a CDU command:
- Left, if valid
- Centre, if left not valid
- Right, if left and centre not valid.
The CDU is the primary control and display interface for the FMCF. The CDU is used to enter flight plan data and performance data. The CDU can also be used to manually tune the navigation radios and access maintenance pages.
- b) Heading Hold (HDG HOLD/Track hold (TRK HOLD)
Pushing the Heading/Track Hold switch selects Heading or Track hold. In this mode, the aircraft holds either heading (HDG) or track (TRK). If the HDG/TRK display on the MCP shows TRK, the aircraft holds track. If the HDG/TRK display on the MCP shows HDG, the aircraft holds heading.
Figure 1.6EB Lateral Mode Switches and Indicators - b) Heading select (HDG SEL)/Track select (TRK SEL)
- Pushing the Heading/Track Select switch (inner) selects Heading select or Track select modes. In this mode, the aircraft turns to the heading or track that shows in the heading/track window. Pushing the Heading/Track (HDG/TRK) Reference switch alternately changes the heading/track reference between heading and track. Rotating the Heading/Track selector (middle) sets the heading or track in the heading/track window. If the HDG/TRK display shows HDG, the aircraft goes to and holds the heading that shows in the heading/track window. If the HDG/TRK display shows TRK, the aircraft goes to and holds the track that shows in the heading/track window. Rotating the Bank Limit selector (outer) sets the bank limit when in the Heading select or Track select modes. In the AUTO position, the limit varies between 15 - 25 degrees, depending on True Airspeed. When the other detented positions are selected, the value is the maximum, regardless of airspeed.
1.6E.2.2 Pitch Modes
The following AFDS pitch modes are available during climb, cruise and descent (Figure 1.6EC below).
- a) Vertical navigation (VNAV)
- Pushing the VNAV switch arms, selects or disarms the VNAV mode. The VNAV mode is a mix of throttle and elevator commands that control the vertical flight path. The FMCF vertical steering commands come from the active FMCF based on the navigation data and the active flight plan.
- b) Vertical speed (V/S)/Flight Path Angle (FPA)
Pushing the V/S-FPA switch selects the V/S or FPA mode. Rotating the V/S-FPA selector Up or Down sets the vertical speed or flight path angle in the vertical speed/flight path angle window. Pushing the V/S-FPA Reference switch alternately changes vertical speed/flight path angle window references between vertical speed and flight path angle. The vertical speed or flight path angle command is an elevator command. The pilot uses this mode to change flight levels. The pilot must set the engine thrust necessary to hold the vertical speed or flight path angle command. When the V/S/FPA display shows V/S, the aircraft goes to and holds the vertical speed that shows on the vertical speed/flight path angle window.
Figure 1.6EC Vertical Mode Switches and Indicators - c) Flight Level Change (FLCH)
- Pushing the FLCH switch selects the Flight level change speed mode. The FLCH command is a mix of thrust and elevator commands to change flight levels. When the IAS/MACH display shows IAS, the elevator command holds the speed that shows on the IAS/MACH window. When the IAS/MACH display shows MACH, the elevator command holds the MACH that shows on the IAS/MACH window. Rotating the IAS/MACH selector sets the speed in the IAS/MACH window. Pushing the IAS/MACH Reference switch alternately changes the IAS/MACH window between IAS and MACH. The Thrust Management Computing Function (TMCF) supplies the engine thrust commands.
- d) Altitude Hold (ALT)
- Pushing the Altitude Hold switch selects the Altitude hold mode. In this mode, the aircraft holds the barometric altitude present when the pilot pushes the altitude HOLD switch.
1.6E.2.3 Landing Modes
The following AFDS functions are available for landing:
- a) Localizer (LOC)
- The LOC mode captures and holds the aircraft to a localizer flight path.
- b) Glideslope (G/S)
- The G/S mode captures and holds the aircraft to a vertical descent flight path.
- c) Flare (FLARE)
- The flare mode controls the aircraft to a smooth touchdown at a point past the glideslope antenna. This is a computed command and is not part of the glideslope mode.
- d) Runway Alignment
- In crosswind conditions, the runway alignment mode supplies roll and yaw control to decrease the aircraft crab angle for touchdown. The runway alignment mode also includes roll and yaw control for an engine failure in approach during autoland.
- e) Rollout (ROLLOUT)
- After touchdown, the rollout mode controls the aircraft to the runway centre line. Aircraft deviation from the localizer centre line supplies rudder and nose wheel steering signals.
- f) Go-Around (TO/GA)
The go-around mode controls roll and pitch after an aborted approach. Also, the TMCF controls thrust during go-around.
Pushing the Localizer (LOC) switch arms, disarms or captures the localizer as roll mode. Pushing the Approach (APP) switch arms, disarms or captures the localizer as roll mode and glidepath (G/S) as pitch mode (Figure 1.6DD below).
Figure 1.6ED Approach Mode Switches
Source: Malaysian ICAO Annex 13 Safety Investigation Team for MH370, 8 March 2015, Factual Information MH370/01/15
The Factual Information was updated in 2018 by the Safety Investigation Report MH370/01/2018 which added new content but did not include all of the previous data.