Go-around altitude constraint
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Go-around altitude constraint
Good evening,
For airbus 330/340 during Go around phase, will the FMGC respect the altitude constraint coded on the go around part on the FM for both GA track mode as well as NAV mode? For example if the FM coding is 3000 feet and FCU is set on 5000 feet. Will it level off at 3000 feet initially?
For airbus 330/340 during Go around phase, will the FMGC respect the altitude constraint coded on the go around part on the FM for both GA track mode as well as NAV mode? For example if the FM coding is 3000 feet and FCU is set on 5000 feet. Will it level off at 3000 feet initially?
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It's not what is in the MCDU but what vertical mode you get in GA that decides whether constraints will be respected. CLB
mode is not available in GA and in OP CLB constraints won't be honoured.
mode is not available in GA and in OP CLB constraints won't be honoured.
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From my FCOM...
The flight crew can arm the CLB mode during the takeoff, go-around, climb, and cruise phases and engage it during the climb and cruise phases.
The CLB mode is armed:
In flight, when the climb or go-around phase is active, and the following conditions are met:
• The lateral NAV mode is engaged
• The FCU selected altitude is above the aircraft's present altitude and the aircraft captures or flies an altitude constraint.
Which means.... If you select NAV before GA ACC ALT, then CLB will be armed, and will engage at ACC ALT.
But.. you cannot engage CLB manually in GA flight phase.
The flight crew can arm the CLB mode during the takeoff, go-around, climb, and cruise phases and engage it during the climb and cruise phases.
The CLB mode is armed:
In flight, when the climb or go-around phase is active, and the following conditions are met:
• The lateral NAV mode is engaged
• The FCU selected altitude is above the aircraft's present altitude and the aircraft captures or flies an altitude constraint.
Which means.... If you select NAV before GA ACC ALT, then CLB will be armed, and will engage at ACC ALT.
But.. you cannot engage CLB manually in GA flight phase.
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Just set the FIRST altitude constraint as the FCU Missed Approach Altitude (assuming you are talking about a complex missed approach procedure like KSEA that has you cross a fix "at or below" a certain altitude, and then continue climb to your holding altitude). That way, no matter what vertical mode you wind up in you will hit the constraint properly. Technique.
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Tyro
When in approach phase moment you hit TOGA FMGC goes to GA phase. In GA phase CLB mode is not available also it does not do any predictions. Simply changing lateral mode to NAV will not give you constraint protection. You need to get out of GA mode by activating approach only then you can get CLB and subsequent constraints protection.
When in approach phase moment you hit TOGA FMGC goes to GA phase. In GA phase CLB mode is not available also it does not do any predictions. Simply changing lateral mode to NAV will not give you constraint protection. You need to get out of GA mode by activating approach only then you can get CLB and subsequent constraints protection.
Last edited by vilas; 8th Aug 2014 at 06:17.
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vilas
Read the FCOM again.....
In GA phase you cannot engage CLB by pushing ALT knob.
However FCOM is quite clear that CLB mode will be armed during GA phase if certain conditions are met.
And if armed CLB will engage automatically if certain other condition are met....
Read the FCOM again.....
In GA phase you cannot engage CLB by pushing ALT knob.
However FCOM is quite clear that CLB mode will be armed during GA phase if certain conditions are met.
And if armed CLB will engage automatically if certain other condition are met....
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Tyro
Read which ever way you want to but as long as you are in GA mode at acceleration altitude you only change to OP CLB from SRS.
PRO-NORM-SRP-01-80 P 1/8
In the GO-AROUND phase, the system makes no predictions. Consequently, CLB and DES modes are not available, and the flight crew must monitor constraints.
Read which ever way you want to but as long as you are in GA mode at acceleration altitude you only change to OP CLB from SRS.
PRO-NORM-SRP-01-80 P 1/8
In the GO-AROUND phase, the system makes no predictions. Consequently, CLB and DES modes are not available, and the flight crew must monitor constraints.
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Tyro there is no way you will get a managed vertical mode (CLB) in a phase of flight where you have no predictions (GA), hence no CLB in GA phase.
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One of the conditions for CLB is that it has to be in a specific performance phases, GA phase not included.
The FCOM seems contradictory because it shows graphics of FMAs with TOGA/SRS/GA TRK and CLB in blue below SRS. However when you accelerate it will be OP CLB, not CLB what you will get. Hence the need to select the first constraint.
It is an old subject of debate, but lately it has become popular. probably there was an incident for this reason… Problem is that now some people misinterpret it and is doing weird things, like setting 1,000 as the GA altitude because the MAP says "climb to 1,000 then turn right to ZZZ VOR climbing to 3000"
.
The FCOM seems contradictory because it shows graphics of FMAs with TOGA/SRS/GA TRK and CLB in blue below SRS. However when you accelerate it will be OP CLB, not CLB what you will get. Hence the need to select the first constraint.
It is an old subject of debate, but lately it has become popular. probably there was an incident for this reason… Problem is that now some people misinterpret it and is doing weird things, like setting 1,000 as the GA altitude because the MAP says "climb to 1,000 then turn right to ZZZ VOR climbing to 3000"
.
