Airbus Comfort Mode??
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Join Date: Apr 2003
Location: Australia
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Airbus Comfort Mode??
I recently noticed an A340 transiting through our airspace with an oscillating Mode C 340-341-340. When queried, the pilot said they were operating in a 'Comfort' Mode on cruise which allowed the aircraft to deviate up and down about +/-50' for passenger comfort. I have never heard of this before, any Airbus drivers out there that can confirm this feature and maybe clarify how it works? Thanks in advance
Don't fly the bus but my guess is a turbulence mode is engaged. An auto flight system reacts to altitude excursions at a particular rate. The corrections can be somewhat abrupt especially in short coupled, rapid wave activity. This can be uncomfortable to the pax, and could inhibit the ability to sleep in the case you observed. With the turb mode on, in general terms the AP reacts a bit slower to return to assigned altitude, making the ride/corrections a bit smoother but taking a bit more altitude to do so.
FWIW, the automation may at lower altitudes deselect the turb mode itself, or the pilots hopefully will deselect it when not needed or when approaching the terminal environment. The mode (on some acft) will also reduce the rate of turn if selected on. In the terminal area (where it should be off) If you notice an aircraft turning to an assigned heading slowly, or starting a turn to intercept a course earlier than what you might expect, ask them if the turb mode is on. The answer of course will be no, followed immediately by an increased rate of turn after they turn it off.
FWIW, the automation may at lower altitudes deselect the turb mode itself, or the pilots hopefully will deselect it when not needed or when approaching the terminal environment. The mode (on some acft) will also reduce the rate of turn if selected on. In the terminal area (where it should be off) If you notice an aircraft turning to an assigned heading slowly, or starting a turn to intercept a course earlier than what you might expect, ask them if the turb mode is on. The answer of course will be no, followed immediately by an increased rate of turn after they turn it off.
The MD80 autopilot used to allow altitude fluctuations of up to 300 feet plus or minus from selected altitude in cruise.
This was not only a turbulence mitigation feature but also a fuel saving concept, if speed was a little low the autopilot would drop the nose slightly allowing speed to increase without moving the autothrottles 'sacrificing' a little altitude to achieve this.
Conversely, with updaft turbulence the autopilot allowed a positive excursion of up to 300 feet.
Of course, this was all in the days before RVSM, can't allow this anymore
This was not only a turbulence mitigation feature but also a fuel saving concept, if speed was a little low the autopilot would drop the nose slightly allowing speed to increase without moving the autothrottles 'sacrificing' a little altitude to achieve this.
Conversely, with updaft turbulence the autopilot allowed a positive excursion of up to 300 feet.
Of course, this was all in the days before RVSM, can't allow this anymore
Join Date: Jan 2001
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FCOM 1
This is on all (I think) FBW Airbus types, and is not a "special" mode selected by the crew... but used on every flight where the aircraft is cruising at (but not below) the FMC programmed Cruise Alt...
NoD
SOFT ALTITUDE
On reaching the planned cruise altitude, ALT CRZ engages and A/THR maintains the speed/mach target.
Two minutes after ALT CRZ engages, if the mach mode is operative, SOFT ALT mode engages. This allows the aircraft to deviate ± 50 feet from the target altitude, thereby minimizing thrust variations and reducing fuel consumption.
On reaching the planned cruise altitude, ALT CRZ engages and A/THR maintains the speed/mach target.
Two minutes after ALT CRZ engages, if the mach mode is operative, SOFT ALT mode engages. This allows the aircraft to deviate ± 50 feet from the target altitude, thereby minimizing thrust variations and reducing fuel consumption.
NoD
Join Date: May 2002
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My 'favourite' feature of the Airbus is cutting the corner at waypoints for the passengers comfort where my 8-10 mile trail quickly becomes a very skinny 5 miles.
Make that waypoint a flyover point, especially when cutting the corner infringes military restricted areas.
Gotta love the frogs.
Make that waypoint a flyover point, especially when cutting the corner infringes military restricted areas.
Gotta love the frogs.
