Automation questions - BOEING

[zhtm475]

To all 737, 747-400, 777 pilots,

I urgently need answers for the following questions regarding Boeing (737, 747-400, 777) aircraft for my human factors research project.

(1). During an ILS approach and when autopilot is engaged:
If the glideslope signal is lost above 1,500 feet, is this correct that the glideslope indicator and FD bars disappear from the ADI, and the aircraft continues its descent at the current rate of descent. But glide slope loss below 1,500 feet results in all autopilot disengaging and in changes in the mode indications (“FLARE armed” is not annunciated).

(2). Is this correct that the go-around mode only available when descending below 2,000 feet RA with auto-throttles armed?

(3). Is this correct that when autopilot is engaged:
The mode control panel (MCP) window is, the last step in the altitude change process, to be changed after the clearance has been received. The autoflight system will not depart the MCP altitude, even if the FMS is programmed for a different altitude.

(4). When autopilot is engaged and V/S mode is used for a climb or descent:
If excessive rate of climb or descent is used and result in a potential of over-speeding or stalling the aircraft, will the automation automatically reverts to the “LVL CHG” mode to protect the target airspeed?

(5). When autopilot is engaged during an ILS approach:
If a go-around is initiated by hitting the TOGA button and autopilot remains engaged, does the aircraft fly the defaulted “runway track” before you hitting the LNAV or HDG SEL?

(6). When aircraft is manually flown with at least one FD on while on “LVL CH” mode, but pilot fails to follow the FD bars (i.e. when the pilot is not descending quick enough to achieve the descent rate shown on the horizontal FD bar). This will obviously results in a decrease in airspeed. If the pilot lets this situation continue and the speed continues to decrease and approach stalling, will the automation do anything to avoid stalling the aircraft or the pilot is the last defence?

(7). Could you explain “VNAV Speed” and “VNAV Path” descent mode logic briefly in terms of its (speed and rate of descent) targets, protections, and operational logic?

[OzExpat]

"human factors"? :eek:

[zhtm475]

The automation problems listed above could reult in the loss of situation and system (mode) awareness, hence they are highly "human factors" related.:cool:

[Intruder]

747-400

(1). During an ILS approach and when autopilot is engaged:
If the glideslope signal is lost above 1,500 feet, is this correct that the glideslope indicator and FD bars disappear from the ADI, and the aircraft continues its descent at the current rate of descent. But glide slope loss below 1,500 feet results in all autopilot disengaging and in changes in the mode indications (“FLARE armed” is not annunciated).

I have not seen this failure, and it is not specifically addressed in training. However, Aerosim (PC-based FMS simulator) shows a reversion to heading hold with loss of LOC; there is no loss of FD bars. I could not simulate a loss of G/S on Aerosim, but a logical reversion would be to V/S at the rate of descent at time of G/S loss.

FLARE and ROLLOUT would disarm at loss of G/S, and LAND 3 should revert to NO AUTOLAND.

I don't know why the autopilot would disengage, though the EICAS and aural warnings at disconnect would be unmistakable.


(2). Is this correct that the go-around mode only available when descending below 2,000 feet RA with auto-throttles armed?

No. TOGA is armed with flaps out of UP or G/S captured.


(3). Is this correct that when autopilot is engaged:
The mode control panel (MCP) window is, the last step in the altitude change process, to be changed after the clearance has been received. The autoflight system will not depart the MCP altitude, even if the FMS is programmed for a different altitude.

Not always. When G/S is captured, MCP altitude is disregarded by the autopilot.


(4). When autopilot is engaged and V/S mode is used for a climb or descent:
If excessive rate of climb or descent is used and result in a potential of over-speeding or stalling the aircraft, will the automation automatically reverts to the “LVL CHG” mode to protect the target airspeed?

There is no speed protection or reversion of any kind in V/S.


(5). When autopilot is engaged during an ILS approach:
If a go-around is initiated by hitting the TOGA button and autopilot remains engaged, does the aircraft fly the defaulted “runway track” before you hitting the LNAV or HDG SEL?

Yes.


(6). When aircraft is manually flown with at least one FD on while on “LVL CH” mode, but pilot fails to follow the FD bars (i.e. when the pilot is not descending quick enough to achieve the descent rate shown on the horizontal FD bar). This will obviously results in a decrease in airspeed. If the pilot lets this situation continue and the speed continues to decrease and approach stalling, will the automation do anything to avoid stalling the aircraft or the pilot is the last defence?

The speed change cannot be assumed if autothrottles are engaged. They will attempt to maintain MCP-commanded speed.

Airspeed EICAS/aural warnings will be made, and stick shaker will warn of high AOA, but the pilot has to make the corrective action.


(7). Could you explain “VNAV Speed” and “VNAV Path” descent mode logic briefly in terms of its (speed and rate of descent) targets, protections, and operational logic?

In VNAV SPEED the autopilot uses pitch (elevator) input to maintain FMS-calculated or MCP-selected speed. Throttles (auto or manual) will control rate of climb/descent.

In VNAV PATH the autopilot uses pitch (elevator) input to keep the airplane on the ideal vertical path. The FMS calculates the "controlling" altitude in the flight plan as entered, and the most efficient way to get there (CLIMB THRUST climb, ECON cruise speed, and IDLE descent). Target speed is maintained +/- 15 KIAS, and buffet margins and gear/flap limit speeds are protected.

[zhtm475]

Dear Intruder,

Thanks for all the infomation. Just want to confirm:

(1) Is your information based on a real 744 SOP/manual or the PC based Aerosim only?

(2) Regarding question 5 about the "track" when GA is initiated during an approach, does the aircraft fly the actual runway track or whatever track it is at the time you hit the TOGA button?

Cheers ;)

[lonerider]

zhtm475,

Question 5- the aircraft actually holds the track at the time of TOGA engagement.

[Intruder]

The answer to Q1 is from Aerosim, because I don't have an airplane or real simulator in my back yard. The answers to the others are from my FHB and experience.

To clarify my answer to Q5, the track during a coupled ILS approach will be the ILS track as published in the approach plates. it may not be exactly the runway heading (but should be, in most cases). TOGA will retain that track if engaged during the approach.

[zhtm475]

I am confused about the "RWY track" and "whatever track it is" when the TOGA button is pushed! Anyone can clarify this? Is it different between 777, 744 and 737?

Also I've got two more questions here (more straight forward this time):

1. Will changing the landing runway erase all previously entered altitude constraints (those requested by ATC, not those in the STAR) in the FMS?

2. Is this true that “LVL CH” and “V/S” mode does not honour altitude constraints programmed into the FMS? However “VNAV” has altitude constraint protection.

Many thanks!!:confused:

[Intruder]

zhtm:

"I am confused about the "RWY track" and "whatever track it is" when the TOGA button is pushed! Anyone can clarify this? Is it different between 777, 744 and 737?"

I can only speak for the 747-400.

The question was in regard to a coupled ILS approach. The track followed by the FMS and autopilot on an ILS approach IS the ILS track. When an ILS is tuned, a magnetic track must also be programmed. When the ILS approach is selected from the DEP/ARR page on the CDU, the ILS freq and track are automatically programmed into the radios and FMS. Once the Approach Mode is armed and engaged, the ILS track is followed. That is the same track that will be followed in the TOGA mode, until another roll mode is selected (above 500' HAA, by our FHB).


"Also I've got two more questions here (more straight forward this time):

"1. Will changing the landing runway erase all previously entered altitude constraints (those requested by ATC, not those in the STAR) in the FMS? "

If a VFR Runway is selected on the DEP/ARR page, no waypoints or altitude constraints will be changed or erased; the runway waypoint will be inserted after the last waypoint on the current route.

If an instrument approach procedure (VOR/LOC/ILS) is selected, any previously-selected approach procedure will be erased and overwritten. If a AP (STAR) is already selected, and that AP is also available for the new runway, its waypoints and altitudes will remain intact. However if the same AP is re-selected, any manually-entered altitude constraints will be deleted when the AP is overwritten.

In either case, no waypoints before the AP will be affected.


"2. Is this true that “LVL CH” and “V/S” mode does not honour altitude constraints programmed into the FMS? However “VNAV” has altitude constraint protection. "

FLCH and V/S use MCP-entered altitude only.

VNAV honors FMS-entered altitude constraints, except where the MCP altitude is more restrictive (e.g., descending from FL330, next programmed constraint is 11,000'; if MCP is set at 15,000', VNAV will level at 15,000' until a lower MCP altitude is entered; if MCP is set at 8,000', VNAV will intercept the constraining waypoint at or above 11,000).

[zhtm475]

Thanks Intruder for all the information.

Any 737 or 777 pilots can anwser the following two questions:

1. When G/A button is pressed, the aircraft will fly the actual track flown over the ground when G/A is initiated, OR follow the ILS track programmed in the FMS.


2. When G/S signal is lost after captured (due to ground equipment failure) for the rest of the approach, aircraft continues descent at the rate when the signal is lost. Will the vertical mode displayed in the PFD changes from G/S to V/S?

Cheers!!
:cool: