Quote71.01. EGPWS mode 6 alerts are now inhibited when parking brake is set.
Hardy, would you have any more data on this? The park brake is mentioned in none of the documents I have on the EGPWS (FCOM, AMM, Engineering Training Notes, Wiring Diagrams). As far as I know, the park brake only
enables the altitude alert system (i.e. the C-chord as you get close to the MCP selected altitude).
Why would you need an inhibit on Mode 6 callouts when Radio Altitude is required to arm the warnings?
A customer (real 744 operator) requested that the EGPWS callouts for minima etc. should be muted when they are set during preflight, e.g. when setting the baro minimum marker for use as a certain takeoff phase marker. E.g. when the aircraft is parked at 1000 ft MSL and you wind it up from below 0 to +3000 ft, the aircraft will -- avionic-wise -- descend through this moving marker and trigger the callout.
I think it's a fact that it should be muted during preflight.
However, the solution with the parking brake is a theory of mine. As we know, the parking brake is also involved in the MCP ALT alert logic (just vice versa: it inhibits the inhibit by G/S or landing flaps). So, using the parking brake for such things is not unusual.
I can offer another theory: They are muted for 2 seconds when the minima knob has been turned. But this may just delay the callout which is not fine; and if the delay disables it completely until the next reset-by-climb, there is a risk that callouts are disabled in flight when doing late changes.
QuoteA customer (real 744 operator) requested that the EGPWS callouts for minima etc. should be muted when they are set during preflight, e.g. when setting the baro minimum marker for use as a certain takeoff phase marker.
Interesting. Thanks!
I have the feeling that the park brake would be very inefficient. The park brake is not alway set (especially if the brakes are cooling on a turnaround). The EGPWS computer only sends audio signals to the MAWEA which amplifies them and sums them with the other aurals before sending them to the aural warning speakers. The EGPWS computer does not send specific data on a bus. Therefore, a park brake inhibit would have to be done by sending a park brake signal to the EGPWS computer.
On regular aircraft, the park brake sends (hardwire/discrete) signals to the Brake System Control Unit (nowhere near the EGPWS computer) and the EIUs (closer to the EGPWS computer). The EIUs do talk to the EGPWS computer for certain things, but unless the EGPWS computer manufacturer already had this modification in mind and could be programmed with software changes, it would be a very expensive modification.
Do you think the operator could shed more light on this?
Where does the EGPWS get the flap and gear status data from, for example? From the EIUs?
|-|ardy
Maybe the inhibit signal from the stall warning computer is also used for ground operations in some way. On the ground the airspeed is typically below stall speed. There is no red tape and no stall alert obviously, but some sort of information in this sense might still be available to the EGPWS in some way?
|-|ardy
QuoteWhere does the EGPWS get the flap and gear status data from, for example? From the EIUs?
Flap position (>/= 25 units) comes from the Left and Centre FCU via wires (discretes). The FCUs and EGPWS are on the equipment racks, so not more than 4 or so meters of wiring.
Gear lever information comes from the gear lever via a long wire from the cockpit (discrete).
QuoteMaybe the inhibit signal from the stall warning computer is also used for ground operations in some way.
Maybe. There is a databus going from the stall warning cards in the MAWEA. Again it would require some foresight of the modification (to be enabled with, say, EGPWS computer software programming). If there was foresight, then it could have been done with Rad Alt, ADC, Mawea (stall warning), etc, databus inputs.
Quote from: John H Watson on Wed, 13 Mar 2019 22:53
Flap position (>/= 25 units) comes from the Left and Centre FCU via wires (discretes).
(Just checked, it's the same in PSX.)
That parking brake criterium is now replaced by SWC inputs in PSX 10.72:
http://aerowinx.com/board/index.php?topic=4191.0
|-|ardy