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Difference between revisions of "Circling Approach - difference between ICAO PANS-OPS and US TERPS"

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[[Aerodrome Operating Minima|Aerodrome operating minima]] (AOM) are calculated by operators based on information supplied by national authorities in their [[AIP]]s.  This information typically consists of approach and departure procedures which assure safe separation between the aircraft and known obstacles located close to the procedure in question.  These procedures are based on obstacle domains constructed using internationally accepted standards.   
+
[[Aerodrome Operating Minima|Aerodrome operating minima]] (AOM) are calculated by operators based on information supplied by national authorities in their [[AIP]]s.  This information typically consists of approach and departure procedures which assure safe separation between the aircraft and known obstacles located close to the procedure in question.  These procedures are based on obstacle clearance domains constructed using internationally accepted standards.   
  
 
Two main sets of procedures exist:
 
Two main sets of procedures exist:
  
*[[ICAO]] Procedures, described in ICAO Doc 8168 Procedures for Air Navigation Services (PANS-OPS).  PANS-OPS procedures are the international standard and are used throughout Europe and in most other countries world-wide.
+
*[[ICAO]] Procedures, described in ICAO Doc 8168 Procedures for Air Navigation Services (PANS-OPS).  PANS-OPS procedures are the international standard and are used throughout Europe and in many other countries world-wide.
 
    
 
    
 
*US Terminal Instrument Procedures (TERPS), described in FAA Directive No 8260.3B.  US TERPS are used in USA and in certain other countries. These include Canada, Korea, Saudi Arabia and Taiwan. Some NATO military procedures are also based on US TERPS standards.
 
*US Terminal Instrument Procedures (TERPS), described in FAA Directive No 8260.3B.  US TERPS are used in USA and in certain other countries. These include Canada, Korea, Saudi Arabia and Taiwan. Some NATO military procedures are also based on US TERPS standards.
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== Circling Approaches ==
 
== Circling Approaches ==
  
'''Minimum Visibility'''
+
===Minimum Visibility===
  
 
Both PANS-OPS and US TERPS assume values of minimum visibility available to the pilot at the lowest obstacle clearance altitude (OCA). These values are calculated differently and therefore, may result in different AOM. Table 1 shows the lowest value of visibility assumed by each method:
 
Both PANS-OPS and US TERPS assume values of minimum visibility available to the pilot at the lowest obstacle clearance altitude (OCA). These values are calculated differently and therefore, may result in different AOM. Table 1 shows the lowest value of visibility assumed by each method:
  
{| cellpadding="20" cellspacing="0" border="1"
+
{| {{Prettytable}}
 +
|+ align="bottom" | Table 1: Minimum Visibility at OCA
 
|Aircraft category
 
|Aircraft category
 
|A
 
|A
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|-
 
|-
 
|Minimum Visibility
 
|Minimum Visibility
PANS-OPS (Km)
+
PANS-OPS
|1.9
+
|[[Distance::1.9 km]]
|2.8
+
|[[Distance::2.8 km]]
|3.7
+
|[[Distance::3.7 km]]
|4.6
+
|[[Distance::4.6 km]]
|6.5
+
|[[Distance::6.5 km]]
 
|-
 
|-
 
|Minimum Visibility
 
|Minimum Visibility
US TERPS (Km)
+
US TERPS
|1.6
+
|[[Distance::1.6 km]]
|1.6
+
|[[Distance::1.6 km]]
|2.4
+
|[[Distance::2.4 km]]
|3.2
+
|[[Distance::3.2 km]]
|3.2
+
|[[Distance::3.2 km]]
 
|}
 
|}
  
:Table 1: Minimum Visibility at OCA
+
===Minimum Obstacle Clearance (MOC)===
 +
ICAO PANS-OPS uses a varying MOC which increases with aircraft category as shown in Table 2:
  
 
+
{| {{Prettytable}}
'''Minimum Obstacle Clearance (MOC)'''
+
|+ align="bottom" | Table 2: Minimum Obstacle Clearance (MOC) - PANS-OPS
 
+
*ICAO PANS-OPS uses a varying MOC which increases with aircraft category as shown in Table 2:
+
 
+
{| cellpadding="20" cellspacing="0" border="1"
+
 
|Aircraft category
 
|Aircraft category
 
|A
 
|A
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|E
 
|E
 
|-
 
|-
|Obstacle Clearance m (ft)
+
|Obstacle Clearance
|90 (295)
+
|[[Length::295 ft]]
|90 (295)
+
|[[Length::295 ft]]
|120 (394)
+
|[[Length::394 ft]]
|120 (394)
+
|[[Length::394 ft]]
|150 (492)
+
|[[Length::492 ft]]
 
|}
 
|}
  
:Table 2: Minimum Obstacle Clearance (MOC) - PANS-OPS
+
US TERPS uses [[Length::300 ft]] as MOC for all aircraft categories.
  
US TERPS uses 300 ft as MOC for all aircraft categories.
+
Thus the pilot of a Category D aircraft carrying out a circling procedure using TERPS minima would have [[Length::94 ft]] less obstacle clearance than using PANS-OPS procedures.
  
Thus the pilot of a Category D aircraft carrying out a circling procedure using TERPS minima would have 94ft less obstacle clearance than using PANS-OPS procedures.
+
===Radius of Circling Domain===
 
+
Both systems use a radius of the circling domain, Obstacle Evaluation Area for US TERPS and Visual Manoeuvring Area for PANS-OPS, that increases with aircraft category and is based on TAS and bank angle. Both systems assume a [[Speed::25 kt]] wind factor, always added as a constant, without an assumption for the direction of the wind.
 
+
'''Radius of Circling Domain:'''
+
 
+
*Both systems use a radius that increases with aircraft category and is based on TAS and bank angle. Both systems assume a 25 kt wind factor.
+
  
 
Aircraft Category is based on threshold IAS (1.3 x Stall IAS) and is shown on Table 3:
 
Aircraft Category is based on threshold IAS (1.3 x Stall IAS) and is shown on Table 3:
  
{| cellpadding="20" cellspacing="0" border="1"
+
{| {{Prettytable}}
 +
|+ align="bottom" | Table 3: Aircraft Category - PANS-OPS and US TERPS
 
|Aircraft Category
 
|Aircraft Category
 
|A
 
|A
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|E
 
|E
 
|-
 
|-
|Threshold IAS (kt)
+
|Threshold IAS  
|less than 91
+
|less than [[Speed::91 kts]]
|91 or more but less than 121
+
|[[Speed::91 kts]] or more but less than [[Speed::121 kts]]
|121 or more but less than 141
+
|[[Speed::121 kts]] or more but less than [[Speed::141 kts]]
|141 or more but less than 166
+
|[[Speed::141 kts]] or more but less than [[Speed::165 kts]]
|165 or more (but less than 211)*
+
|[[Speed::166 kts]] or more (but less than [[Speed::211 kts]])*
 
|}
 
|}
 
For PANS OPS only*
 
For PANS OPS only*
:Table 3: Aircraft Category - PANS-OPS and US TERPS
 
  
  
 
For PANS-OPS, the TAS is based on aircraft altitude and the visual manoeuvring IAS (Circling IAS). The latter is shown on Table 4:
 
For PANS-OPS, the TAS is based on aircraft altitude and the visual manoeuvring IAS (Circling IAS). The latter is shown on Table 4:
  
{| cellpadding="20" cellspacing="0" border="1"
+
{| {{Prettytable}}
 +
|+ align="bottom" | Table 4: Visual Manoeuvring IAS used by PANS-OPS
 
|Aircraft Category
 
|Aircraft Category
 
|A
 
|A
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|E
 
|E
 
|-
 
|-
|Circling IAS (kt)
+
|Circling IAS
|100
+
|[[Speed::100 kts]]
|135
+
|[[Speed::135 kts]]
|180
+
|[[Speed::180 kts]]
|205
+
|[[Speed::205 kts]]
|240
+
|[[Speed::240 kts]]
 
|}
 
|}
  
:Table 4: Visual Manoeuvring IAS used by PANS-OPS
 
  
 
For US TERPS, TAS calculation is based on aircraft altitude and threshold IAS appropriate to category (shown on Table 3).   
 
For US TERPS, TAS calculation is based on aircraft altitude and threshold IAS appropriate to category (shown on Table 3).   
  
  
PANS-OPS assumes a bank angle of 20° for aircraft of all categories. US TERPS assumes a bank angle which varies with aircraft category, but is never less than 20 ° - see Table 5:
+
PANS-OPS assumes a bank angle of 20° for aircraft of all categories. US TERPS assumes a bank angle which varies with aircraft category, but is never less than 20° - see Table 5:
  
{| cellpadding="20" cellspacing="0" border="1"
+
{| {{Prettytable}}
 +
|+ align="bottom" | Table 5: Bank Angle used by US TERPS
 
|Aircraft Category
 
|Aircraft Category
 
|A
 
|A
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|22
 
|22
 
|}
 
|}
 
:Table 5: Bank Angle used by US TERPS
 
  
  
 
Because the IAS used for TAS calculation is greater and the assumed bank angle is lower, the radius of the circling area used in PANS-OPS is larger than that used in US TERPS. This means that an obstacle within the assumed circling area calculated using PANS-OPS criteria might fall outside the obstacle area calculated using US TERPS.
 
Because the IAS used for TAS calculation is greater and the assumed bank angle is lower, the radius of the circling area used in PANS-OPS is larger than that used in US TERPS. This means that an obstacle within the assumed circling area calculated using PANS-OPS criteria might fall outside the obstacle area calculated using US TERPS.
  
This is believed to have been a major factor in the following fatal accident, which resulted in considerable loss of life:  
+
This is believed to have been a major factor in the following fatal accident, which resulted in considerable loss of life: [[B762, vicinity Busan Korea, 2002 (CFIT HF)]]
 
+
*[[B762, vicinity Busan Korea, 2002 (CFIT HF)]]
+
  
 
Additionally, pilots not aware of the increased bank angle expected in US TERPS calculations might in certain circumstances stray outside the circling area due to the increased circling radius.
 
Additionally, pilots not aware of the increased bank angle expected in US TERPS calculations might in certain circumstances stray outside the circling area due to the increased circling radius.
  
In summary, circling procedures based on US TERPS calculations afford considerably lower safety margins than those based on ICAO PANS-OPS. It is therefore essential that pilots understand these differences and are aware of the basis of calculations for all airfields at which they intend to operate. The basis for calculation of minima is usually printed on the approach plate (see Further Reading: Jeppesen Chart Basics - a presentation).
+
In summary, circling procedures based on US TERPS calculations afford considerably lower safety margins than those based on ICAO PANS-OPS. It is therefore essential that pilots understand these differences and are aware of the basis of calculations for all airfields at which they intend to operate, including alternates. The basis for calculation of minima is usually printed on the approach plate (see Further Reading: Jeppesen Chart Basics - a presentation).
  
 
National authorities or operators may require adjustments to be applied to operating minima to compensate for these differences.
 
National authorities or operators may require adjustments to be applied to operating minima to compensate for these differences.
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== Related Articles ==
 
== Related Articles ==
 
 
*[[Aerodrome Operating Minima]]
 
*[[Aerodrome Operating Minima]]
 
*[[Approach and Landing Risks]]
 
*[[Approach and Landing Risks]]
 +
*[[Circling Approach]]
  
 
== Further Reading ==
 
== Further Reading ==
 
+
*[http://skybrary.aero/bookshelf/books/1486.pdf Circling Approach Discussion Paper], FSF European Advisory Committee, 24 January 2011
Note: some of these references may refer to pre-Change 21 versions of US TERPS.
+
 
+
 
*ICAO Doc 8168: Procedures for Air Navigation Services - Aircraft Operations (PANS-OPS), Volume II: Construction of Visual and Instrument Flight Procedures
 
*ICAO Doc 8168: Procedures for Air Navigation Services - Aircraft Operations (PANS-OPS), Volume II: Construction of Visual and Instrument Flight Procedures
 
 
*[http://www.faa.gov/regulations_policies/orders_notices/index.cfm/go/document.information/documentID/11698 US FAA Directive 8260.3B Standards for Terminal Instrument Procedures (TERPS) Including Change 21]  
 
*[http://www.faa.gov/regulations_policies/orders_notices/index.cfm/go/document.information/documentID/11698 US FAA Directive 8260.3B Standards for Terminal Instrument Procedures (TERPS) Including Change 21]  
 
 
*[http://www.skybrary.aero/bookshelf/books/1430.PDF TERPS Review - Circle to Land Tactics]
 
*[http://www.skybrary.aero/bookshelf/books/1430.PDF TERPS Review - Circle to Land Tactics]
 
 
*[http://www.skybrary.aero/bookshelf/books/1429.pdf TERPS Review - Circling and the Visual Segment]
 
*[http://www.skybrary.aero/bookshelf/books/1429.pdf TERPS Review - Circling and the Visual Segment]
 
 
*[http://www.skybrary.aero/bookshelf/books/1431.pdf Jeppesen Chart Basics - a presentation]
 
*[http://www.skybrary.aero/bookshelf/books/1431.pdf Jeppesen Chart Basics - a presentation]
 
 
*[http://www.skybrary.aero/bookshelf/books/1432.pdf Circling Traps - a presentation]
 
*[http://www.skybrary.aero/bookshelf/books/1432.pdf Circling Traps - a presentation]
 +
*Article: [http://www.terps.com/ifrr/jun98.pdf "TERPS, CFIT and me" from June 1998 edition of "IFR Refresher" magazine]
  
*Article: [http://www.terps.com/ifrr/jun98.pdf "TERPS, CFIT and me" from June 1998 edition of "IFR Refresher" magazine]
+
'''''Note''''': ''Some of these references refer to pre-Change 21 versions of US TERPS.''
  
 
[[Category:Operational Issues]]
 
[[Category:Operational Issues]]
 
[[Category:Controlled Flight Into Terrain]]
 
[[Category:Controlled Flight Into Terrain]]
 
[[Category:Glossary]]
 
[[Category:Glossary]]

Revision as of 13:08, 17 April 2011

Article Information
Category: General General
Content source: SKYbrary About SKYbrary
Content control: EUROCONTROL EUROCONTROL

Comparison between ICAO PANS-OPS and US TERPS

Aerodrome operating minima (AOM) are calculated by operators based on information supplied by national authorities in their AIPs. This information typically consists of approach and departure procedures which assure safe separation between the aircraft and known obstacles located close to the procedure in question. These procedures are based on obstacle clearance domains constructed using internationally accepted standards.

Two main sets of procedures exist:

  • ICAO Procedures, described in ICAO Doc 8168 Procedures for Air Navigation Services (PANS-OPS). PANS-OPS procedures are the international standard and are used throughout Europe and in many other countries world-wide.
  • US Terminal Instrument Procedures (TERPS), described in FAA Directive No 8260.3B. US TERPS are used in USA and in certain other countries. These include Canada, Korea, Saudi Arabia and Taiwan. Some NATO military procedures are also based on US TERPS standards.

Pilots should be aware that there are significant differences in obstacle clearance criteria between procedures designed in accordance with ICAO PANS-OPS and US TERPS. This is especially true in respect of Circling Approaches where the assumed radius of turn and minimum obstacle clearance are markedly different (see below). US TERPS Change 21 (May 2009) introduced measures which have reduced the differences between the two methods, nevertheless, significant differences remain.

Circling Approaches

Minimum Visibility

Both PANS-OPS and US TERPS assume values of minimum visibility available to the pilot at the lowest obstacle clearance altitude (OCA). These values are calculated differently and therefore, may result in different AOM. Table 1 shows the lowest value of visibility assumed by each method:

Table 1: Minimum Visibility at OCA
Aircraft category A B C D E
Minimum Visibility

PANS-OPS

1.9 km1.026 nm
1,900 m
6,233.596 ft
2.8 km1.512 nm
2,800 m
9,186.352 ft
3.7 km1.998 nm
3,700 m
12,139.108 ft
4.6 km2.484 nm
4,600 m
15,091.864 ft
6.5 km3.51 nm
6,500 m
21,325.459 ft
Minimum Visibility

US TERPS

1.6 km0.864 nm
1,600 m
5,249.344 ft
1.6 km0.864 nm
1,600 m
5,249.344 ft
2.4 km1.296 nm
2,400 m
7,874.016 ft
3.2 km1.728 nm
3,200 m
10,498.688 ft
3.2 km1.728 nm
3,200 m
10,498.688 ft

Minimum Obstacle Clearance (MOC)

ICAO PANS-OPS uses a varying MOC which increases with aircraft category as shown in Table 2:

Table 2: Minimum Obstacle Clearance (MOC) - PANS-OPS
Aircraft category A B C D E
Obstacle Clearance 295 ft89.916 m 295 ft89.916 m 394 ft120.091 m 394 ft120.091 m 492 ft149.962 m

US TERPS uses 300 ft91.44 m as MOC for all aircraft categories.

Thus the pilot of a Category D aircraft carrying out a circling procedure using TERPS minima would have 94 ft28.651 m less obstacle clearance than using PANS-OPS procedures.

Radius of Circling Domain

Both systems use a radius of the circling domain, Obstacle Evaluation Area for US TERPS and Visual Manoeuvring Area for PANS-OPS, that increases with aircraft category and is based on TAS and bank angle. Both systems assume a 25 kt46.3 km/h
12.85 m/s
wind factor, always added as a constant, without an assumption for the direction of the wind.

Aircraft Category is based on threshold IAS (1.3 x Stall IAS) and is shown on Table 3:

Table 3: Aircraft Category - PANS-OPS and US TERPS
Aircraft Category A B C D E
Threshold IAS less than 91 kts168.532 km/h
46.774 m/s
91 kts168.532 km/h
46.774 m/s
or more but less than 121 kts224.092 km/h
62.194 m/s
121 kts224.092 km/h
62.194 m/s
or more but less than 141 kts261.132 km/h
72.474 m/s
141 kts261.132 km/h
72.474 m/s
or more but less than 165 kts305.58 km/h
84.81 m/s
166 kts307.432 km/h
85.324 m/s
or more (but less than 211 kts390.772 km/h
108.454 m/s
)*

For PANS OPS only*


For PANS-OPS, the TAS is based on aircraft altitude and the visual manoeuvring IAS (Circling IAS). The latter is shown on Table 4:

Table 4: Visual Manoeuvring IAS used by PANS-OPS
Aircraft Category A B C D E
Circling IAS 100 kts185.2 km/h
51.4 m/s
135 kts250.02 km/h
69.39 m/s
180 kts333.36 km/h
92.52 m/s
205 kts379.66 km/h
105.37 m/s
240 kts444.48 km/h
123.36 m/s


For US TERPS, TAS calculation is based on aircraft altitude and threshold IAS appropriate to category (shown on Table 3).


PANS-OPS assumes a bank angle of 20° for aircraft of all categories. US TERPS assumes a bank angle which varies with aircraft category, but is never less than 20° - see Table 5:

Table 5: Bank Angle used by US TERPS
Aircraft Category A B C D E
Bank Angle (degrees) 25 25 20 20 22


Because the IAS used for TAS calculation is greater and the assumed bank angle is lower, the radius of the circling area used in PANS-OPS is larger than that used in US TERPS. This means that an obstacle within the assumed circling area calculated using PANS-OPS criteria might fall outside the obstacle area calculated using US TERPS.

This is believed to have been a major factor in the following fatal accident, which resulted in considerable loss of life: B762, vicinity Busan Korea, 2002 (CFIT HF)

Additionally, pilots not aware of the increased bank angle expected in US TERPS calculations might in certain circumstances stray outside the circling area due to the increased circling radius.

In summary, circling procedures based on US TERPS calculations afford considerably lower safety margins than those based on ICAO PANS-OPS. It is therefore essential that pilots understand these differences and are aware of the basis of calculations for all airfields at which they intend to operate, including alternates. The basis for calculation of minima is usually printed on the approach plate (see Further Reading: Jeppesen Chart Basics - a presentation).

National authorities or operators may require adjustments to be applied to operating minima to compensate for these differences.

Some other less significant differences exist between ICAO PANS-OPS and US TERPS. For details refer to the relevant documents listed below.

Related Articles

Further Reading

Note: Some of these references refer to pre-Change 21 versions of US TERPS.