Investigate Operational Use of Level Restrictions in SIDs, STARs and other Published Routes

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Investigate Operational Use of Level Restrictions in SIDs, STARs and other Published Routes

49TH ANNUAL CONFERENCE, Punta Cana, Dominican Republic, 12-16 April 2010

WP No. 88

Investigate Operational Use of Level Restrictions in SIDs, STARs and other Published Routes

Presented by TOC

Summary

In November 2007, ICAO introduced Amendment 5 to ICAO Doc 4444 (PANS-ATM). This amendment contained revised procedures and phraseologies associated with climb and descent instructions issued to aircraft following a SID or a STAR. Although the goal was to harmonize these procedures, several counties have not introduced, or only partly introduced these new procedures and phraseologies. As pilots are flying all over the world, experiencing different procedures and phraseologies, this has resulted in a serious safety hazard.

This working paper examines the new procedures and phraseology as well as SID and STAR design and proposes new IFATCA Policy.

Introduction

1.1  In November 2007 amendment 5 to ICAO Doc 4444 (PANS-ATM) was introduced containing revised procedures and phraseology associated with climb and descent instructions issued to aircraft following a SID or a STAR. This amendment has not been as successful as intended. Concerns have been raised about the different treatment of cancelling requirements to comply with published restrictions on these routes.

1.2  Differences between the en-route environment versus the terminal environment are experienced. Also differences between countries in procedures and associated phraseologies regarding the status of published altitude restrictions on standard instrument departure (SID) and standard terminal arrival (STAR) procedures when further altitude clearances are issued by air traffic control.

1.3  This paper first describes the background of the amendment and all issues since the amendment was introduced. Subsequently it proposes a way forward.

1.4  This work was originally proposed to be included with agenda item “Study Routes Clearances and Associated Requirements” but was split at the 2009 Conference in Dubrovnik.

1.5  This study has been done in close cooperation with IFALPA.

Discussion

2.1 Background

2.1.1  In 2003 ICAO Headquarters issued a clarification confirming that all level restrictions needed to be re-stated in order to remain in effect. However, this generated a problem for many Air Navigation Service Providers (ANSPs), in particular regarding levels in SIDs and STARs.

2.1.2  In 2003 the Eurocontrol ATM Procedures Development Sub-Group (APDSG) proposed that, in the absence of suitable ICAO provisions, there was a potential for deviations from level restrictions published as elements of SIDs and STARs. This was considered to be due to differing interpretations by controllers and pilots as to the continuing validity of SID/STAR level restrictions when subsequent clearances to climb or descend were given.

2.1.3  Following a workshop in 2005, APDSG agreed that a full safety assessment should be conducted and ICAO documents should include suitable provisions to ensure a common understanding that level restrictions published as part of a SID or STAR remain in force unless explicitly cancelled by ATC. During 2006 APDSG members and Eurocontrol conducted the required safety assessment.

2.1.4  In 2006 ICAO issued a State Letter proposing amending ICAO Doc 4444 (PANS-ATM) procedures relating to climb clearances above levels specified in a SID and descent clearances below levels specified in a STAR. ICAO received 60 responses from States and international organizations.

  • IATA, IFATCA and Eurocontrol all supportive and many States and organizations suggested that there was a need to state explicitly that the SID/STAR level restrictions were cancelled.
  • IFALPA response recognized the proposal as a means of resolving the current ambiguity.
  • FAA comments highlighted that the proposed phraseology would also impact on other ICAO Annexes and Documents.
  • The UK was the only state to object in principle against the fundamental change.

2.1.5  In June 2007 ICAO issued a State Letter to inform all States that the ANC approved amendment 5 to Doc 4444 by 22 November 2007. This amendment included revised procedures relating to climb and descent instructions to aircraft following a SID or a STAR.


2.2 The revised procedures introduced in ICAO Doc 4444 in November 2007 are as follows:

2.2.1 Aircraft on a SID

6.3.2.4 CLIMB CLEARANCE ABOVE LEVELS SPECIFIED IN A SID

Note. — See also 11.4.2.6.2.5.

When a departing aircraft on a SID is cleared to climb to a level higher than the initially cleared level or the level(s) specified in a SID, the aircraft shall follow the published vertical profile of a SID, unless such restrictions are explicitly cancelled by ATC.

2.2.2  Flight crews operating on a SID, which includes level restrictions at specific waypoints must always comply with these level restrictions unless such restrictions are explicitly cancelled by ATC.

2.2.3  When the level restrictions are explicitly cancelled the ICAO phraseology is (ICAO Doc 4444 paragraph 12.3.1.2(z)):

CLIMB TO (level) [LEVEL RESTRICTION(S) (SID designator) CANCELLED (or) LEVEL RESTRICTION(S) (SID designator) AT (point) CANCELLED].

For example:

KLM1234 CLIMB TO FLIGHT LEVEL 230 LEVEL RESTRICTIONS WOODY 1 S DEPARTURE CANCELLED

Or:

KLM1234 CLIMB TO FLIGHT LEVEL 230 LEVEL RESTRICTIONS WOODY 1 S DEPARTURE AT LEKKO CANCELLED

2.2.4  Level restrictions, which are not explicitly cancelled by ATC, remain in effect. This means that the aircraft should follow the vertical profile of the SID completely before climbing to a higher cleared level.

2.2.5  When the level restrictions are not explicitly cancelled the ICAO phraseology is (ICAO Doc 4444 paragraph 12.3.1.2(a)):

CLIMB TO (level).

For example:

KLM1234 CLIMB TO FLIGHT LEVEL 230

2.2.6  Aircraft on a STAR

6.5.2.4 DESCENT BELOW LEVELS SPECIFIED IN A STAR

Note. — SEE ALSO 11.4.2.6.2.5.

When an arriving aircraft on a STAR is cleared to descend to a level lower than the level or the level(s) specified in a STAR, the aircraft shall follow the published vertical profile of a STAR, unless such restrictions are explicitly cancelled by ATC. Published minimum levels based on terrain clearance shall always be applied.

2.2.7 Flight crews operating on a STAR, which includes level restrictions at specific waypoints must always comply with these level restrictions unless such restrictions are explicitly cancelled by ATC.

2.2.8  When the level restrictions are explicitly cancelled the ICAO phraseology is (ICAO Doc 4444 paragraph 12.3.1.2(aa)):

DESCEND TO (level) [LEVEL RESTRICTION(S) (STAR designator) CANCELLED (or) LEVEL RESTRICTION(S) (STAR designator) AT (point) CANCELLED].

For example:

KLM1234 DESCENT TO FLIGHT LEVEL 100 LEVEL RESTRICTIONS NORKU 2 A ARRIVAL CANCELLED

Or:

KLM1234 DESCENT TO FLIGHT LEVEL 100 LEVEL RESTRICTIONS NORKU 2 A ARRIVAL AT SONSA CANCELLED

2.2.9  Level restrictions, which are not explicitly cancelled by ATC, remain in effect. This means that the aircraft should follow the vertical profile of the STAR completely before descending to a lower cleared level.

2.2.10  When the level restrictions are not explicitly cancelled the ICAO phraseology is (ICAO Doc 4444 paragraph 12.3.1.2(a)):

DESCENT TO (level).

For example:

KLM1234 DESCENT TO FLIGHT LEVEL 100

2.2.11  In addition to this procedure for a STAR, minimum levels based on terrain clearance must always be applied.

2.2.12  Level restrictions issued by ATC

11.4.2.6.2.5 Level restrictions issued by ATC in air-ground communications shall be repeated in conjunction with subsequent level clearances in order to remain in effect.

2.2.13  In all cases, level restrictions issued by ATC in air-ground communications shall be repeated by ATC in conjunction with subsequent level clearances in order to remain in effect.

For example:

First transmission:

KLM1234 CLIMB TO FLIGHT LEVEL 140 CROSS LEKKO FLIGHT LEVEL 60 OR ABOVE

Second transmission:

KLM1234 CLIMB TO FLIGHT LEVEL 210 CROSS LEKKO FLIGHT LEVEL 60 OR ABOVE

2.2.14 In any case a level restriction issued by ATC in air-ground communications is not repeated by ATC, these level restrictions are no longer valid.

For example:

First transmission:

KLM1234 CLIMB TO FLIGHTLEVEL 140 CROSS LEKKO FLIGHT LEVEL 60 OR ABOVE

Second transmission:

KLM1234 CLIMB TO FLIGHT LEVEL 210


2.3 Experiences

2.3.1  At many airports SID’s contain a flight level restriction. This is subject to inbound traffic descending on top. Clear of the inbound flow, outbound traffic is cleared to higher level. The following experiences have been observed:

  • Aircraft leveling off to complete the vertical profile of the SID before climbing to a higher level. This is according the new procedures.
  • Aircraft climbing straight away to a higher level, ignoring the vertical profile of the SID. If the level restrictions are not explicitly cancelled, this is against the new ICAO provisions.
  • Flight crew confirming if they should comply with the level restrictions or should continue the climb straight away. This causes extra RT-load.

2.3.2  Once level restrictions of the SID are explicitly cancelled, confusion could arise about level restrictions further down the route. For example level restrictions on the boundary of two areas of responsibility could be ignored once the level restrictions of the SID are cancelled.

2.3.3  Sweden have received several reports regarding aircraft arriving on a STAR that after having been given “cleared approach” from ATC descends through the published level restrictions on the STAR. This happened while the level restrictions of the STAR are not explicitly cancelled.

2.3.4  The USA has not implemented the new procedure.

2.3.5  The Netherlands changed the description of all SID’s. Instead of a level restriction of “At FL60” it now states “At FL60 or above, if instructed by ATC”.

This has resulted in more clarity for pilots as pilots will not level of at FL 60. However, the original level restriction was intended to protect outbound traffic from inbound traffic descending to FL 70. The change which was made also changed the design and the intention of the SID.

2.3.6 The UK issued procedures and guidance regarding SIDs, pending further safety analysis of the revised ICAO procedures. The interim guidance was that controllers should adhere to the existing UK procedures when issuing amendments to clearances, with the addition of the word ‘now’ to climb clearances above the SID profile.

For example:

KLM1234 CLIMB NOW FL 120


2.4 Current initiatives

2.4.1  In 2007 Eurocontrol issued a Safety Warning Message specifically relating to the revised procedures, highlighting the impending change and potential for misinterpretation. Eurocontrol also issued a pamphlet summarizing the changes along with others that formed Amendment 5 to PANS-ATM.

2.4.2  In light of the evidence that there is room for different interpretations, the ICAO ANB decided to circulate an ICAO State Letter for gathering from States concerns with regards the application of the provisions in question. A copy of ICAO State Letter AN 13/2.1-09/25 is attached in Appendix A.

2.4.3  IFATCA replied to ICAO that they are experiencing little consistency worldwide. Some states have implemented the new procedures; some have partly and some not at all. IFATCA recognizes that the differences are caused by different SID and STAR design around the world as SIDs and STARs can serve different purposes.

2.4.4  IFALPA also replied to ICAO that they are experiencing little consistency worldwide. Some States fully implemented the revised procedures, some not at all and some where some airports have and some have not. IFALPA emphasizes that this is not acceptable to flight crew who operate globally. To operate to the highest safety standard possible ICAO should ensure that procedures are harmonized and phraseology standardized.

2.4.5 A UK safety assessment identified to following safety concerns:

2.4.5.1  Established ICAO procedures for aircraft not on a SID or a STAR state:

“level restrictions issued by ATC in air-ground communications shall be repeated in conjunction with subsequent level clearances in order to remain in effect”.

The revised procedures have introduced a meaning which is opposite of that. Flight crews need to assess in which phase of flight they are to apply the correct procedures.

2.4.5.2  The revised procedures have introduced a form of conditional clearance without the conditions explicitly stated on RT. Therefore, adherence to the conditions of the clearance relies on flight crew applying the correct procedures.

2.4.5.3  Flight crews applying incorrect procedures for that phase of flight result in a level bust. This could be safety critical, especially in busy TMA airspace.

2.4.5.4  The terms used could lead to misinterpretation:

  • ‘Levels specified in a SID/STAR’ – uncertainty has been expressed whether this applies only to level associated with waypoints.
  • ‘Vertical profile of a SID/STAR’ – uncertainty has been expressed whether the vertical profile ends at the last waypoint that has an explicit altitude, or at the final waypoint.

2.4.5.5  As the vertical profile of a SID has a safety function it usually does not reflect the most expeditious climb. Providing the best service to airlines, the revised procedures result in a significant increase in RT load. It should be noted that there are a significant number of SID designators in use in complex TMA airspace with multiple runways and airports.

2.4.5.6  In case the revised procedures would be reversed, this would result in the need for level restrictions to be reiterated when necessary. However, such phraseology already exists (ICAO Doc 4444 paragraph 12.3.2.4) and would result in a smaller increase comparing to the current situation.


2.5 The way forward

2.5.1  At the first TOC Meeting in Las Vegas a combined session with the IFALPA ATS committee was organized to discuss this subject. Both committees agreed this issue is a safety hazard caused by different SID and STAR design around the world. SIDs and STARs should be harmonized in the future ATM system.

2.5.2  Both committees acknowledged that a global redesign of SID’s and STAR’s would be unlikely to happen in the near future. Moreover, ICAO has no intention to rollback the changes in Amendment 5.

2.5.3  Subsequently, both committees focussed on the phraseology. The current phraseology to cancel restrictions is experienced too long and increases R/T load. On the other hand, the phraseology does not emphasize to follow restrictions. Although this should not be necessary according to the new procedures, it would mitigate the risk, which is caused by the little consistency worldwide.

2.5.4  To emphasize that level restrictions in a SID or STAR remain valid the following phraseology was discussed:

CLIMB TO FL… VIA SID/STAR

2.5.5  In case the level restrictions in a SID or STAR are cancelled several alternatives were discussed. The phraseology: CLIMB TO FL … UNRESTRICTED could indicate that other restrictions, ie. speed restrictions, would be cancelled as well. After discussion, the following phraseology was discussed:

OPEN CLIMB TO FL …

This phraseology is related to terminology already used by Airbus in its FMS operations and most importantly is easy to pronounce.

2.5.6  Discussion on the exact phraseology has not finished at this moment and it’s not the intention of this paper to propose the best phraseology. The phraseology should make it absolutely clear whether level restrictions in SIDs or STARs should be followed or not.

Conclusions

3.1  Responses to the ICAO State letter on SID and STAR phraseology have indicated a safety hazard exists in relation to level changes on SIDs and STARs.

3.2  This whole issue is caused by poorly harmonized SID and STAR design around the globe. To solve all problems concerning level restrictions in SID’s and STAR’s a global redesign would be necessary. SID’s and STAR’s should be designed in the same way all around the world.

3.3  As it is unlikely that a global redesign of SID’s and STAR’s will happen in the near future, a short-term solution should be found the cope with the current (unsafe) situation. It should be absolutely clear to pilots whether level restrictions on a SID or STAR should be followed or not.

3.4  The current ICAO phraseology is too long and seems unworkable. For the short term, where the current ICAO procedures remain valid, new phraseology should be developed which is easier to use. This should encourage a globally harmonized way of working, according to the procedures in Amendment 5.

Recommendations

4.1 IFATCA Policy is:

SID and STAR design and use should be globally harmonized.

and is included on page 3 2 3 28 of the IFATCA Technical and Professional Manual.

4.2  IFATCA Policy is:

Phraseology should be developed to easily indicate whether published vertical restrictions and requirements are to be followed or not.

and is included on page 3 2 3 28 in the IFATCA Technical and Professional Manual.

4.3  IFATCA Policy is:

All level change clearances for aircraft on SIDs and STARs shall explicitly indicate whether published vertical restrictions and requirements are to be followed or not.

and is included on page 3 2 3 28 in the IFATCA Technical and Professional Manual.

Last Update: September 29, 2020  

April 15, 2020   306   Jean-Francois Lepage    2010    

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