SID/STAR Phraseology

SID/STAR Phraseology

57TH ANNUAL CONFERENCE, Accra, Ghana, 19-23 March 2018

WP No. 87

SID/STAR Phraseology

Presented by TOC

Summary

New ICAO SID/STAR-Phraseology has been introduced in some countries with some problems arising. This working paper gives an overview of existing IFATCA policies and regulations, compares their advantages and drawbacks, and proposes improvements to policies and phraseology.

Introduction

1.1 The objective of this working paper is to review existing IFATCA policies and regulations. The following paragraphs list all IFATCA policies mentioning SID or STAR and quotes the existing major documents dealing with SID/STAR phraseologies.

1.2 These regulations will then be examined and evaluated and the most promising regulation will be the baseline to check our policies against.

Discussion

2.1 During recent years, SID and STAR design has increased in complexity and led to countries developing their own rules and phraseologies without “management” by ICAO. This unsatisfactory situation led IFATCA and IFALPA to push for harmonized rules and phraseology by ICAO, as this meant less ambiguity. After a lengthy process, ICAO finalised a new set of phraseology which was introduced in November 2016. However, the USA opted not to introduce the new phraseology, other countries have been slow with the introduction and in some countries, the implementation was not flawless. Therefore, at the previous IFATCA conference in May 2017, TOC was tasked with reviewing the current status-quo and applicable IFATCA policies.

2.2 At this point in time there seem to be 3 major different types of phraseology in use around the world (https://www.nbaa.org/ops/intl/nam/canada-sid-star/): 15th-Edition-ICAO, FAA, 16th-Edition-ICAO.

The following quotes from the mentioned manuals illustrate the different phraseologies. The 15th edition of ICAO Doc 4444 does not provide phraseology for continuous descent operations on a STAR. Doc 9931 (CDO Manual) lists a few examples in use in various countries in appendix 2 of said document.

CLIMB/DESCEND followed as necessary by TO (level);

6.3.2.4 CLIMB CLEARANCE ABOVE LEVELS SPECIFIED IN A SID

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.

6.5.2.4 DESCENT BELOW LEVELS SPECIFIED IN A STAR

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.

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.

(ICAO Doc 4444 15th Edition, 2007, page 118 and 121)

 

CDO PHRASEOLOGY EXAMPLES

Note 1 – Phraseologies and associated procedures described in this Appendix are used by at least one State as a means of accomplishing CDO.

Note 2 – The need for clear, concise and unambiguous phraseologies in controller-pilot communications applies equally to CDO. ICAO is currently analysing proposals addressing concerns which have been identified related to the PANS-ATM SID/STAR provisions. It is intended that any new provisions would take into consideration CDO. […]

2. A “descend via” clearance may be issued on procedures with defined altitude crossing points and/or defined speeds. A descend via clearance is an instruction to the pilot to descend in a manner that complies with the published lateral flight path, altitudes and speeds. Because lateral and vertical flight paths are known, a “descend via” clearance may be given well in advance of the actual descent point. […]

2.1 A “descend via” differs from a “descend at pilot’s discretion”, because a “descend via” has vertical and lateral navigation, altitudes and speeds to be complied with, whereas a “descend at pilot’s discretion” has no boundaries that are defined in the procedure. Therefore the “descend via” profile is known in advance to ATC and pilots, adding predictability to the procedure. “Descend via” instructions to vertically navigate on a STAR with published restrictions.

PHRASEOLOGY:

DESCEND VIA (designator)

EXAMPLES:

“Descend via KODAP1A.”

“Cross ABC intersection at flight level two four zero, then descend via COAST TWO Arrival.”

TERMINAL: “Descend via the RIIVR TWO Arrival, after RIIVR, cleared ILS runway two five left”

Note 1 – Clearance to “descend via” authorizes pilots:

a) to vertically and laterally navigate on a STAR; and

b) when cleared to a waypoint depicted on an instrument flight procedure, to descend from a previously assigned altitude at “pilot’s discretion” to the altitude depicted for that waypoint, and once established on the depicted arrival, to navigate laterally and vertically to meet all published restrictions.

Note 2 – ATC is responsible for obstacle clearance when issuing a “descend via” clearance from a previously assigned level.

Note 3 – Pilots navigating on an instrument approach or arrival procedure shall maintain last assigned level until receiving clearance to “descend via”. […]

(ICAO DOC 9931 1st Edition, 2010, appendix 2)

 

2.3 The phraseology contained in the 15th edition of ICAO Doc 4444 does not provide the necessary unambiguous tools required for SID and STAR procedures. There is no prescribed phraseology for cancellation of restrictions or re-joining the SID/STAR. The inconsistency of implementation and application led to interpretations of the phraseology, which in turn led to assumptions being made by the pilot and/or air traffic controller (IFALPA Safety Bulletin 13SAB003, 6.12.2012). Continuous Descend Operations (CDO) are often put into practice with an optimized descent profile which is normally associated with a STAR to allow maximum practical use of a CDO. (ICAO CDO-Manual Doc 9931 1st Edition 2010, Page 16)

2.4 For CDO only examples of existing phraseologies are quoted. These examples do not provide phraseology for leaving a continuous descent, cancellation of speed/level restrictions among others and are clearly not globally harmonized. The 15th edition Phraseology lacks the potential for a harmonised ruleset for CDO on STARs and lead to the unacceptable potential for a loss of separation. (IFALPA Safety Bulletin 13SAB003, 6.12.2012)

2.5 FAA JO 7110.65W 4-5-7, 2015-12-10:

Instructions to vertically navigate on a STAR/SID with published crossing restrictions.

CLIMB/DESCEND VIA (SID/STAR name and number)

If it is necessary to assign a crossing altitude which differs from the STAR or SID altitude, emphasize the change to the pilot.

DESCEND VIA (STAR name and number) ARRIVAL, EXCEPT CROSS (fix, point, waypoint), (revised altitude information).

When an aircraft has been issued an interim altitude and after departure ATC can subsequently clear the aircraft to climb to the original top altitude published in a SID that contains published crossing restrictions, instruct aircraft to “climb via SID.” When issuing a different altitude and compliance with published restrictions is still required, instruct aircraft to “climb via SID except maintain (altitude).”

CLIMB VIA SID.

CLIMB VIA SID except maintain (altitude).

 

Based on the 15th edition of Doc 4444, the FAA built phraseology that is tailored to the needs of a single country. An advantage is the clear distinction, that any climb or descend clearance only modifies the vertical trajectory of the aircraft. It does not rely on stating a level when clearing a SID/STAR. For many countries, this approach is not acceptable because it introduces the possibility for vertical movement to an unwanted and unsafe level. Since ICAO charting according to Annex 4, Chapter 9 does not prescribe levels on SID charts, this ruleset would lead to a great deal of work when redesigning the charts. Furthermore, the use of non-ICAO phraseology e.g. “EXCEPT MAINTAIN FL 100” (e.g. JO 7110.65W 4-3-2) to cancel charted levels is clearly in conflict with ICAO phraseology. While this ruleset is a clear improvement compared to the 15th editon, it lacks global support and does not interlink with other existing ICAO Annexes.

2.6 AMDT 7, ICAO 2016 edition ICAO Doc 4444 16th Edition, 2016:

4.6.4 SID and STAR

The flight crew shall comply with published SID and STAR speed restrictions unless the restrictions are explicitly cancelled or amended by the controller.

6.3.2.4.1 CLEARANCES ON A SID

Clearances to aircraft on a SID with remaining published level and/or speed restrictions shall indicate if such restrictions are to be followed or are cancelled. The following phraseologies shall be used with the following meanings:

a) CLIMB VIA SID TO (level): […]

b) CLIMB VIA SID TO (level), CANCEL LEVEL RESTRICTION(S): […]

6.5.2.4.1 CLEARANCES ON A STAR

Clearances to aircraft on a STAR with remaining published level and/or speed restrictions shall indicate if such restrictions are to be followed or are cancelled. The following phraseologies shall be used with the following meaning:

a) DESCEND VIA STAR TO (level): […]

b) DESCEND VIA STAR TO (level), CANCEL LEVEL RESTRICTION(S): […]

 

The phraseology in the 16th edition of Doc 4444 was designed to combine the strengths of the FAA phraseology with the general ICAO ruleset. It shares the clear distinction between lateral and vertical trajectory on SIDs and STARs, while staying compatible with other ICAO Annexes.

While the 16th edition phraseology has the support of IFATCA and IFALPA (IFALPA Safety Bulletin 17SAB05 SID and STAR phraseology, 18 May 2017), it was not promptly adopted by the majority of countries and some of the early adopters have run into problems.

Because this phraseology seems to be the most promising system of rules for global adoption, the following paragraphs investigate the mentioned problems and the influence of IFATCA policies against the background of 16th edition Phraseology.


Identified aspects/phrases that can be improved

2.7 Speed Restrictions

Doc 4444 states in 6.3.2.4.1 d) iii) that the phraseology “CANCEL SPEED RESTRICTION(S)” cancels published speed restrictions, but does not explicitly specify which speed restrictions are meant by this. Real life operations have shown that this phraseology can be misunderstood and pilots assume that other speeds, like IAS 250 kts below FL100 are cancelled.

If the controller needs to overrule the published horizontal speeds, e.g. for spacing, and tries to cancel the published speed restrictions, the phrase: “AIRCRAFT CANCEL SPEED RESTRICTIONS FLY IAS 180 kts” does not seem to be the optimal logical solution and it is not clear if a verbal speed restriction overrules future published restrictions. A clarification in 4.6.4 would help to reduce the workload.

IFATCA policies do not mention speed restrictions on SIDs and STARs. They are common on both STARs and SIDs to ensure separation, turn radius or noise abatement and therefore should be mentioned just as self-evidently as vertical rates in the policy.

2.8 Amending or deviating from published SID/STAR-level-restrictions The policy “Published level restrictions remain valid unless explicitly cancelled by ATC.” can lead to unintended results e.g. when using rates to provide separation. If level restrictions have to be cancelled explicitly every time, the phrases can become illogical and complexity is increased to a point where air traffic controllers cannot be expected to be aware of the ramifications of their clearance. A possible solution would be to define the use of rates as explicit cancellation: Instead of “AIRCRAFT DESCEND UNRESTRICTED TO FLIGHT LEVEL 130 AT RATE 2000 ft./min” the shorter phrase “AIRCRAFT DESCEND TO FLIGHT LEVEL 130 AT RATE 2000 ft./min” would lead to the same result and be closer to the phraseology used en-route.

2.9 Reiteration of cleared levels

According to Doc 4444 6.3.2.4.5/6.5.2.4.5 when an aircraft is vectored or cleared to proceed to a point that is not on the SID or STAR, the controller shall reiterate the cleared level. This leads to many seemingly unnecessary reiterations of an unchanged level. Because a clearance involving a level normally is only stated, when a change is involved, these reiterations increase uncertainty in the cockpit instead of removing it.

Depending on the aircraft manufacturer the aircraft’s selected level can be different from the cleared level. For example, in this instance a reiteration could be a welcome reminder of the cleared level, so an addition of the phrase “if necessary” or “if doubt exists” would enable air traffic controllers to generally omit the level and state it if needed. Necessary level restrictions would still have to be confirmed or amended according to 6.3.2.4.5 b) and 6.5.2.4.5 b).

2.10 Standard Inbound/Departure Clearance

The standard inbound clearance (6.5.2.3.) does not reflect the new phraseology (12.3.3.2.) The standard inbound clearance has to include a cleared level according to 6.5.2.3., but the phraseology in 12.3.3.2 does not include one: “CLEARED (designation) ARRIVAL”. Because there is a newly created phraseology in place to take care of vertical movement on a STAR it seems counterproductive to include a level in a standard clearance that should only cover the lateral part of a STAR. This is reinforced by the fact that note 2 (“The use of a STAR designator without a cleared level does not authorize the aircraft to descend on the STAR vertical profile.“) states how to act on receiving a standard clearance without a cleared level.

The standard departure clearance 6.3.2.3. shall include a level as well, which seems intended, but in this case the note 2 appears inconsistent.

2.11 CPDLC/DCL vs. Doc 4444

The ICAO Global Operational Data Link Document does not define the necessary CPDLCmessages for use on SID and STAR with level and/or speed restrictions (ICAO Global Operational Data Link Document GOLD 2nd edition 26 April 2013). The CPDLCstandard descend messages for example are incompatible with 16th edition phraseology. The focus on oceanic use cases resulting in incompatibility with modern continental SIDs and STARs should be fixed in a future version of ICAO’s Global Operational Data Link Document.

Likewise, CPDLC Departure Clearance (DCL) is not equipped to deliver departure clearances that include the correct phrase and information.

2.12 The following paragraphs are a step-by-step breakdown of IFATCA Policies concerning SID/STAR, contained in the Technical and Professional Manual

The IFATCA Technical and Professional Manual states in ATS 3.27 Instrument departures and arrivals:

SID and STAR design and use should be globally harmonized.

(IFATCA Technical and Professional Manual, ATS 3.27 (3 2 3 30) – Resolution B9 – WP 88 – Punta Cana 2010)

 

By definition a harmonized global design has to be designed by ICAO and the 16th edition has the potential to achieve this goal.

IFATCA policy is: Phraseology and corresponding message sets shall be developed to easily indicate whether published vertical profile is to be followed or not.

(IFATCA Technical and Professional Manual, ATS 3.27 (3 2 3 30) – Resolution B9 – WP 91 – Amman 2011)

 

While the message set of the 16th edition phraseology gives examples how to use or not use the published restrictions, feedback from countries that have implemented it already show that deviating from the SID or STAR – e.g. to ensure separation by using vertical rates – can be cumbersome and slower than before.

The reason for this could be the inconsistency between 4.6.4 “The flight crew shall comply with published SID and STAR speed restrictions unless the restrictions are explicitly cancelled or amended by the controller.” and the following paragraphs demanding the use of the phrase “DESCEND VIA STAR” or “CLIMB VIA SID” to ensure compliance.

A similar message set should be used to indicate if published speed restrictions are to be followed or not.

For aircraft on SIDs and STARs, all level change clearances shall explicitly indicate whether the published vertical profile is to be followed or not, provided that controller workload does not increase beyond an acceptable level.

(IFATCA Technical and Professional Manual, ATS 3.27 (3 2 3 30) – Resolution B8 – WP 91 – Amman 2011)

 

As mentioned in the previous paragraph the strict use of 16th edition phraseology can increase controller workload, because the phraseology can be very complex.

Conclusions

3.1 While the intention behind the ICAO 16th-edition phraseology was to harmonize procedures and wording globally. There was no deadline or implementation date set, which contributed to a variety of phraseologies being used around the globe.

3.2 Inconsistency in usage of phraseology can increase confusion and uncertainty for flight crews (IFALPA Safety Bulletin 17SAB05 SID and STAR Phraseology 18 May 2017).

3.3 Implementation in some states has shown that the transition from 15th to 16th edition phraseology can lead to differences in interpretation that may affect safety. Especially the similarity between FAA and 16th edition phraseology seems to be a cause for concern (https://www.wfscorp.com/resources/alerts/general/navcanada-suspends-climbdescend-clearances).

3.4 The design of STARs and SIDs can vary from very simple to extremely complex, depending on the airspace and sector design. The new ICAO phraseology tries to cover every possible aspect of what a pilot shall or shall not do in any certain case (e.g. when vectored of a STAR or SID). This had led to a very complex set of instructions which can increase controller workload beyond an acceptable level. In addition, there are certain cases that are not covered or require cumbersome or seemingly illogical use of phraseology.

Recommendations

4.1 It is recommended that IFATCA policy is:

Airspace, procedures and charting should be designed and implemented based on the latest ICAO provisions regarding SIDs and STARs. The result shall be that ATC clearances are unambiguous and their intended effects are achieved. Controller workload shall not increase beyond and acceptable level.

And is included in the IFATCA Technical and Professional Manual, ATS 3.27 Instrument departures and arrivals.

4.2 It is recommended that IFATCA policy:

Phraseology and corresponding message sets shall be developed to easily cancel published level restrictions.

is deleted from the IFATCA Technical and Professional Manual.

4.3 It is recommended that IFATCA policy:

For aircraft on SIDs and STARs, all level change clearances shall explicitly indicate whether the published vertical profile is to be followed or not, provided that controller workload does not increase beyond an acceptable level .

is deleted from the IFATCA Technical and Professional Manual.

References

IFATCA Technical and Professional Manual

ICAO Global Operational Data Link Document GOLD 2nd edition 26 April 2013

ICAO CDO-Manual Doc 9931 1st Edition 2010

ICAO Doc 4444 15th Edition, 2007

ICAO Doc 4444 16th Edition, 2016

FAA JO 7110.65W 4-5-7, 2015-12-10

IFALPA Safety Bulletin 17SAB05, SID and STAR Phraseology, 18 May 2017

https://www.wfscorp.com/resources/alerts/general/navcanada-suspends-climbdescendclearances Information retrieved: December 2017

Last Update: October 1, 2020  

December 27, 2019   266   Jean-Francois Lepage    2018    

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