Aircraft approach category question
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Aircraft approach category question
"The criteria taken into consideration for the classification of aircraft by categories is the indicated airspeed at threshold (VAT) in landing configuration at the maximum certified landing weight i.e. VAT = 1.3 VS or VAT = 1.23 VS1G (fly-by-wire aircraft)."
I don't quiet understand this, especially the 1.23 VS1G.
Would appreciate some explanation please?
Also while on the topic, I want to understand why an a330 is a CAT C whilst an a321. Is a CAT D?
Thanks in advance guys.
I don't quiet understand this, especially the 1.23 VS1G.
Would appreciate some explanation please?
Also while on the topic, I want to understand why an a330 is a CAT C whilst an a321. Is a CAT D?
Thanks in advance guys.
Last edited by WhySoTough; 12th Dec 2012 at 09:38.
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There you go, wst - simple!
This from a 2009 PPRune post - bear in mind the FCOM reference may be out-of-date
"According to Airbus F-COM 3.04.10
VS or Stalling speed, it is not displayed. Moreover, for a conventional A/c, the reference stall speed, VSmin is based on a load factor that is less than 1g. This gives a stall speed that is lower than than the stall speed at 1g.
All operating speeds are expressed as functions of this speed (for instance VREF = 1.3 VSmin). Because A/c of the A320 family have a low speed protection featute (alpha limit) that the flight crew can not override, the airworthiness authorities have reconsidered the definition of stall speed for these A/c.
All operating speeds must be referenced to a speed that can be demonstrated by flight test. The speed is designated as VS1g. Airworthiness authorities have agreed that a factor of .94 represents the relationship between VS1g for A/c of the A320 family and VSmin for conventional A/c types. As a result tha authorities allow A/c of the A320 family to use the following factors:
V2 = 1.2 * .94 VS1g = 1.13 VS1g
VREF = 1.3 * .94 VS1g = 1.23 VS1g
FCOM concludes by saying that the A319,320,321 hav exactly the same maneuver margin that a conventional A/c would have at its reference speeds."
This from a 2009 PPRune post - bear in mind the FCOM reference may be out-of-date
"According to Airbus F-COM 3.04.10
VS or Stalling speed, it is not displayed. Moreover, for a conventional A/c, the reference stall speed, VSmin is based on a load factor that is less than 1g. This gives a stall speed that is lower than than the stall speed at 1g.
All operating speeds are expressed as functions of this speed (for instance VREF = 1.3 VSmin). Because A/c of the A320 family have a low speed protection featute (alpha limit) that the flight crew can not override, the airworthiness authorities have reconsidered the definition of stall speed for these A/c.
All operating speeds must be referenced to a speed that can be demonstrated by flight test. The speed is designated as VS1g. Airworthiness authorities have agreed that a factor of .94 represents the relationship between VS1g for A/c of the A320 family and VSmin for conventional A/c types. As a result tha authorities allow A/c of the A320 family to use the following factors:
V2 = 1.2 * .94 VS1g = 1.13 VS1g
VREF = 1.3 * .94 VS1g = 1.23 VS1g
FCOM concludes by saying that the A319,320,321 hav exactly the same maneuver margin that a conventional A/c would have at its reference speeds."
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1.23 isn't just for FBW.
CS-25 calls for VSR to be calculated under 1g whereas in the past this wasn't the case.
1.23 VS1g gives the same margin as 1.3 oldschool Vs
CS-25 calls for VSR to be calculated under 1g whereas in the past this wasn't the case.
1.23 VS1g gives the same margin as 1.3 oldschool Vs
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My 2 pence input:
On FBW aircraft Vref is referenced to VS1g instead of VS like on a conventional aircfraft.
As a reminder VS1g speed corresponds on the polar curve to CL max , situated on top of the curve. Whereas Vs speed is situated downwards , lower on the curve.
VS1g is the minimum speed achievable at 1g which means that the aircraft still flies at VS1g and not in a stall like it would be at VS.
Having said that , I would add that the reference used on FBW VS1g, is a higher speed than VS.
Now if the reference speed is higher, then the increment has to be lower in order to keep the same equation
Vref= 1,3 VS
VS=0,94 VS1g
Vref= 1,3x0,94= 1,222 VS1g
Airbus , authorities rounded up and retained 1,23 VS1g
So mathematically speaking 1,23 VS1g is even higher than 1,3 VS.
Practical example:
Aircraft stall speed : 94 kt
Then Vs 1g = 100kt
Vref referenced to VS would give 1,3x94= 122,2 kt
Vref referenced to Vs1g: 1,23x 100 kt=123 kt
Now which one is higher?
So why some people think that 1,23 vs1 g is a lower speed than 1,3 VS?
On FBW aircraft Vref is referenced to VS1g instead of VS like on a conventional aircfraft.
As a reminder VS1g speed corresponds on the polar curve to CL max , situated on top of the curve. Whereas Vs speed is situated downwards , lower on the curve.
VS1g is the minimum speed achievable at 1g which means that the aircraft still flies at VS1g and not in a stall like it would be at VS.
Having said that , I would add that the reference used on FBW VS1g, is a higher speed than VS.
Now if the reference speed is higher, then the increment has to be lower in order to keep the same equation
Vref= 1,3 VS
VS=0,94 VS1g
Vref= 1,3x0,94= 1,222 VS1g
Airbus , authorities rounded up and retained 1,23 VS1g
So mathematically speaking 1,23 VS1g is even higher than 1,3 VS.
Practical example:
Aircraft stall speed : 94 kt
Then Vs 1g = 100kt
Vref referenced to VS would give 1,3x94= 122,2 kt
Vref referenced to Vs1g: 1,23x 100 kt=123 kt
Now which one is higher?
So why some people think that 1,23 vs1 g is a lower speed than 1,3 VS?
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It is not possible by definition to be CAT C for straight in and CAT D for circling, unless your airline has wrongly interpreted Aircraft Category definition.
What determines the aircraft category in which you fall in, is the Vat , which is the speed at threshold called also Vref
You could be doing 160 kts on final or 180 kts in a circling , you are still in C category as long as your Vref is within 121 -140 kts at threshold.
In ICAO document 8168 , There is a range of speeds for each aircraft category depending on the position you are in the approach:
As an exemple for CAT C :
Vat: 121-140 kts
Range of final approach speed:115 - 160 kts
Circling : max speed 180 kts
Initial approach: 160-240 kts
Etc..
So if you are doing 180 kt during circling approach you are still not in D category as , your Vref will still be in the C category when you cross the threshold
Unless you decide to land at 180 , in that case you will be in E !
Also landing fees, are based on Aircraft Category. The higher the category , the higher the landing fees.
But you will not pay a higher price if you were doing 180 kt in circling , as your threshold speed was still the same.
What determines the aircraft category in which you fall in, is the Vat , which is the speed at threshold called also Vref
You could be doing 160 kts on final or 180 kts in a circling , you are still in C category as long as your Vref is within 121 -140 kts at threshold.
In ICAO document 8168 , There is a range of speeds for each aircraft category depending on the position you are in the approach:
As an exemple for CAT C :
Vat: 121-140 kts
Range of final approach speed:115 - 160 kts
Circling : max speed 180 kts
Initial approach: 160-240 kts
Etc..
So if you are doing 180 kt during circling approach you are still not in D category as , your Vref will still be in the C category when you cross the threshold
Unless you decide to land at 180 , in that case you will be in E !
Also landing fees, are based on Aircraft Category. The higher the category , the higher the landing fees.
But you will not pay a higher price if you were doing 180 kt in circling , as your threshold speed was still the same.
So if you are doing 180 kt during circling approach you are still not in D category
Originally Posted by FAA Aeronautical Information Manual
NOTE-
Refer to 14 CFR 91.175 (i).
5-4-7. Instrument Approach Procedures
a. Aircraft approach category means a grouping of aircraft based on a speed of VREF, if specified, or if VREF is not specified, 1.3 VSO at the maximum certified landing weight. VREF, VSO, and the maximum certified landing weight are those values as established for the aircraft by the certification authority of the country of registry. A pilot must use the minima corresponding to the category determined during certification or higher. Helicopters may use Category A minima. If it is necessary to operate at a speed in excess of the upper limit of the speed range for an aircraft's category, the minimums for the higher category must be used. For example, an airplane which fits into Category B, but is circling to land at a speed of 145 knots, must use the approach Category D minimums. As an additional example, a Category A airplane (or helicopter) which is operating at 130 knots on a straight-in approach must use the approach Category C minimums.
Refer to 14 CFR 91.175 (i).
5-4-7. Instrument Approach Procedures
a. Aircraft approach category means a grouping of aircraft based on a speed of VREF, if specified, or if VREF is not specified, 1.3 VSO at the maximum certified landing weight. VREF, VSO, and the maximum certified landing weight are those values as established for the aircraft by the certification authority of the country of registry. A pilot must use the minima corresponding to the category determined during certification or higher. Helicopters may use Category A minima. If it is necessary to operate at a speed in excess of the upper limit of the speed range for an aircraft's category, the minimums for the higher category must be used. For example, an airplane which fits into Category B, but is circling to land at a speed of 145 knots, must use the approach Category D minimums. As an additional example, a Category A airplane (or helicopter) which is operating at 130 knots on a straight-in approach must use the approach Category C minimums.
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So if you are doing 180 kt during circling approach you are still not in D category as , your Vref will still be in the C category when you cross the threshold
CIRCLING approach category has nothing to do with VREF (your aircraft aproach category), it is solely based on the SPEED you are going to fly it.
Last edited by de facto; 13th Dec 2012 at 01:16.
It is not possible by definition to be CAT C for straight in and CAT D for circling, unless your airline has wrongly interpreted Aircraft Category definition.
Last edited by compressor stall; 13th Dec 2012 at 04:53.
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'APPrOaCH category is for straight in and is based on Vref (vat 1.3vso or 1.23 vsr whichever is higher)
CIRCLING approach category has nothing to do with VREF (your aircraft aproach category), it is solely based on the SPEED you are going to fly it.'
I would like to see a reference for this from the country that you're flying in. The only references I have seen define catagory on Vref (based on stall speed at max landing weight).
The wording differs from country to country but most allow operators to choose to fly at a higher catagory to allow the aircraft to be operated at a higher speeds during the approach. Everywhere I have flown also requires you to use a higher catagory if you have a malfunction that drives your Vref up. For example if you are Cat B and have a flap failure then your Vref may now be in Cat C.
CIRCLING approach category has nothing to do with VREF (your aircraft aproach category), it is solely based on the SPEED you are going to fly it.'
I would like to see a reference for this from the country that you're flying in. The only references I have seen define catagory on Vref (based on stall speed at max landing weight).
The wording differs from country to country but most allow operators to choose to fly at a higher catagory to allow the aircraft to be operated at a higher speeds during the approach. Everywhere I have flown also requires you to use a higher catagory if you have a malfunction that drives your Vref up. For example if you are Cat B and have a flap failure then your Vref may now be in Cat C.
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I would like to see a reference for this from the country that you're flying in. The only references I have seen define catagory on Vref (based on stall speed at max landing weight).
CIRCLING category is NOT based on APPROACH categore but on SPEED one is to fly the circle portion of the maneuver.
FAA allows pilots to increase but not decrease their APPROaCH category.
Check FAA docs in their website.
Last edited by de facto; 13th Dec 2012 at 07:50.
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The FAA reference, already quoted above, explains how catagory is determined. It does not say that it does not apply for circling. It does say you can choose to use a higher catagory if you want to take advantage of the higher circling speeds. So even if you can comply with the approach speeds for the catagory you can't drop down a Cat. ie even if you may be flying an aircraft with a Vat of 145 kts and could conceivably fly an approach, including circling, within Cat C speeds that would not be legal. Likewise if your aircraft only just fits into a Cat at max landing weight you can't drop down when at a lower weight.
The is only one type of catagory, that is instrument approach catagory. There is separate circling catagory. Not sure of the legality of operating in one cat for straight-in and another for circling.
The is only one type of catagory, that is instrument approach catagory. There is separate circling catagory. Not sure of the legality of operating in one cat for straight-in and another for circling.
Jeppesen Aus states you can circle at a higher category if you wish provided you comply with the restrictions for the higher category. Basically if you need more room to manoeuvre you can use the larger circling area of a higher category provided you also use the higher obstacle clearance altitude.
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De facto : sorry, but the Cat is not determined with the speed you fly in the portion of the manoeuvre.
Any Category whether A, B , C , or D has a wide variety of speed range to allow flexibility to the operator and the maximum speeds are used to calculate the protection.
Again, a C aircraft can fly up to 180 kts during a circle to land . Please refer to your jeppesen or wikipedia.
I accept the fact that FAA might have different rules. But this is not the case in ICAO, and Eu Ops world.Aircraft category is based on Vref which is the threshold crossing speed, regardless of your downwind speed or circling speed.
Now the example given in your FAA document is not clear:
*"For example, an airplane which fits into Category B, but is circling to land at a speed of 145 kts must use the category D minimum"
Firstly you are not supposed to exceed the maximum speed for your aircraft category, for a circle to land. As previously sated there is a range of speeds within which you must be inside during your approach.
For a CAT B aircraft the maximum speed authorised during a circle to land is 135 kts
For a Cat C aircraft the maximum speed authorised for a circle to land is 180 kts
For a D aircraft the maximum speed authorised for a circle to land is 205 kts
So if your aircraft category is B and you are doing 145 in a circling you are not respecting the speeds for your aircraft category.*
Could be that FAA does not specify a range of speeds for each aircraft category, or a maximum speed in circle to land.. But ICAO does.
Circling to land approaches with PAN OPS criteria , have been designed according to ICAO document 8168 volume 2. Which means they are calculated with Maximum speeds for each category as laid down in the document.
The design is based on the maximum speed for the category. For a C aircraft , the maximum speed in a circle to land is 180 kt. So all margins , areas of protections are designed and based on that maximum speed.
If you are doing lower than 180 kt, you will be inside the protection as your radius will be lower.
I recall a question that many examiners ask during oral test, or type rating : what is the maximum speed allowed in a circle to land for a C aircraft? Answer : 180 kts.
Moreover I have seen many approach charts with pan ops criteria specifying under the circle to land box, the max speed for the category just in front of minimas.
A-->100*
B-->135
C-->180
D-->205
Any Category whether A, B , C , or D has a wide variety of speed range to allow flexibility to the operator and the maximum speeds are used to calculate the protection.
Again, a C aircraft can fly up to 180 kts during a circle to land . Please refer to your jeppesen or wikipedia.
I accept the fact that FAA might have different rules. But this is not the case in ICAO, and Eu Ops world.Aircraft category is based on Vref which is the threshold crossing speed, regardless of your downwind speed or circling speed.
Now the example given in your FAA document is not clear:
*"For example, an airplane which fits into Category B, but is circling to land at a speed of 145 kts must use the category D minimum"
Firstly you are not supposed to exceed the maximum speed for your aircraft category, for a circle to land. As previously sated there is a range of speeds within which you must be inside during your approach.
For a CAT B aircraft the maximum speed authorised during a circle to land is 135 kts
For a Cat C aircraft the maximum speed authorised for a circle to land is 180 kts
For a D aircraft the maximum speed authorised for a circle to land is 205 kts
So if your aircraft category is B and you are doing 145 in a circling you are not respecting the speeds for your aircraft category.*
Could be that FAA does not specify a range of speeds for each aircraft category, or a maximum speed in circle to land.. But ICAO does.
Circling to land approaches with PAN OPS criteria , have been designed according to ICAO document 8168 volume 2. Which means they are calculated with Maximum speeds for each category as laid down in the document.
The design is based on the maximum speed for the category. For a C aircraft , the maximum speed in a circle to land is 180 kt. So all margins , areas of protections are designed and based on that maximum speed.
If you are doing lower than 180 kt, you will be inside the protection as your radius will be lower.
I recall a question that many examiners ask during oral test, or type rating : what is the maximum speed allowed in a circle to land for a C aircraft? Answer : 180 kts.
Moreover I have seen many approach charts with pan ops criteria specifying under the circle to land box, the max speed for the category just in front of minimas.
A-->100*
B-->135
C-->180
D-->205