Summary

Over the past few years, TOC came to the conclusion that the TPM was in need of a significant overhaul in order to ensure consistency throughout the manual and with ICAO. Every year, several slight changes are made to individual policies, but there is a need to look at the entire TPM in a holistic way.

Introduction

1.1. The Surveillance section of the Technical Professional Manual (TPM) consists of two policies; both of which are up for review.

Discussion

2.1. SUR 6.1 – Surveillance Definitions.

2.1.1. Within this section of the document four terms are defined: Surveillance, Independent Surveillance, Dependent Surveillance, and Automatic Dependent Surveillance. These definitions are not included within ICAO Annex 10, Volume IV. The definitions are important to have but their location within the document is called into question. They are better suited in the Acronyms and Terms section rather than within SUR 6.1.

2.2. SUR 6.2 – ADS-B: Single Emergency Code Management.

2.2.1. The paper which leads to the creation of SUR 6.2 was a 2007 working paper was spurred by ICAO 12th Air Navigation Conference. The original paper investigated ADS-B without separate emergency codes just normal SSR targets. This included matters such as hardware issues, losing capability to transmit Squawk Pulse Indicator (SPI) while an emergency code was being transmitted, and issues related to Automatic Dependent Surveillance (ADS) with emergencies.

2.2.1.1. The first paragraph of existing policy states the requirement for ADS-B replacing radar requires it to function at the same level or better than SSR. However, there are still concerns about the use of ADS-B as the sole method of surveillance.

2.2.1.2. Since publication of this paper DO260 has been superseded by DO260B, wherein the new documents have revised requirements and timelines for compliance.

2.2.1.3. The final paragraph of the policy discusses targets without ability to squawk separate emergency codes in a SSR environment would appear as standard targets.

2.2.1.4. While the world works on an equipage level where the ability to simultaneously squawk a discrete emergency and SPI, there is the need to maintain awareness of the issue. In the future it is possible that this will become a non-factor and this policy can be removed.

2.2.2. The first portion of the policy for analysis is, “If ADS-B is to replace radar then it must have the same or better functionality as SSR, and this specifically includes discrete emergency codes and a SPI function.”. The concept is still valid in that the new system must provide the same or better functionality before replacing the previous system in place.

2.2.2.1. From Aircraft Operations, Document 8168, all aircraft with a serviceable transponder must operate it at all times, regardless of whether operating within SSR airspace.

1.1.1 When an aircraft carries a serviceable transponder, the pilot shall operate the transponder at all times during flight, regardless of whether the aircraft is within or outside airspace where secondary surveillance radar (SSR) is used for ATS purposes.

ICAO Document 8168 Vol 1, Chapter 3

2.2.2.2. Additionally, in Document 8168 there are details as to when emergency discrete codes would be utilized.

1.5 COMMUNICATION FAILURE PROCEDURES

The pilot of an aircraft losing two-way communications shall set the transponder to Mode A Code 7600.

Note.— A controller who observes an SSR response indicating selection of the communications failure code will determine the extent of the failure by instructing the pilot to SQUAWK IDENT or to change code. If it is determined that the aircraft receiver is functioning, further control of the aircraft will be continued using code changes or IDENT transmission to acknowledge receipt of clearances. Different procedures may be applied to Mode S equipped aircraft in areas of Mode S coverage.

1.6 UNLAWFUL INTERFERENCE WITH AIRCRAFT IN FLIGHT

1.6.1 If there is unlawful interference with an aircraft in flight, the pilot-in-command shall attempt to set the transponder to Mode A Code 7500 in order to indicate the situation. If circumstances so warrant, Code 7700 should be used instead.

1.6.2 If a pilot has selected Mode A Code 7500 and has been requested to confirm this code by ATC (in accordance with 1.1.5), the pilot shall, according to circumstances, either confirm this or not reply at all.

Note.— If the pilot does not reply, ATC will take this as confirmation that the use of Code 7500 is not an inadvertent false code selection.

ICAO Document 8168 Vol 1, Chapter 3

2.2.2.3. Within the PANS ATM 16th Edition 8.5.4 still notes that the first-generation ADS-B avionics may lack the ability to transmit information beyond the code selected by the pilot.

8.5.4 Operation of ADS-B transmitters

Note 1.— To indicate that it is in a state of emergency or to transmit other urgent information, an aircraft equipped with ADS-B might operate the emergency and/or urgency mode as follows:

a) emergency;
b) communication failure;
c) unlawful interference;
d) minimum fuel; and/or
e) medical.

Note 2.— Some aircraft equipped with first generation ADS-B avionics do not have the capability described in Note 1 above and only have the capability to transmit a general emergency alert regardless of the code selected by the pilot.

2.2.2.4. Due to the most recent edition of PANS ATM still featuring Note 2 in 8.5.4 there is an indication that some older generation avionics are still in use. Therefore, it is proposed that the first section of the policy is kept in place.

2.2.2.5. These issues are further restated within PANS ATM 16th edition in the emergency section.

15.3.2 As soon as it is known that two-way communication has failed, action shall be taken to ascertain whether the aircraft is able to receive transmissions from the air traffic control unit by requesting it to execute a specified manoeuvre which can be observed by an ATS surveillance system or to transmit, if possible, a specified signal in order to indicate acknowledgement.

Note.— Some aircraft equipped with first generation ADS-B avionics do not have the capability of squawking IDENT while the emergency and/or urgency mode is selected.

2.2.2.6. One minor change proposed for continued harmonization with ICAO documentation is changing the word must to shall.

2.2.3. The second portion of existing policy, “In non-radar airspace DO260 ADS-B is considered an acceptable interim solution provided global procedures are established for handling single emergency codes and potentially decreased SPI functionality”, references out of date documentation and requires analysis.

2.2.3.1. The RTCA, formerly known as the Radio Technical Commission for Aeronautics, is a public-private partnership which seeks to balance the interests of both sides while supporting modernization. Existing policy was based on the available information at the time including RTCA Doc 260 and 260A. These papers were superseded in 2011 by DOC 260B. Below is a chart comparing RTCA 260 with its later A and B editions. As the more recent editions of the publication came out, they provided additional information without eliminating any earlier functionality. The later editions are also backwards compatible.

2.2.3.2. The efficiency of any technological advance is due in part to equipage. As the RTCA requirements show above the newer technologies provide more comprehensive information. Honeywell produced a timeline with dates for when compliance with RTCA 260/A/B must be attained by. While obviously not an all-inclusive chart, it does demonstrate some of the worldwide mandates.

2.2.4. Within the SUR6.2 policy paper it lays out the creation of a separate document, Technical Provisions for Mode S Services and Extended Squitter, which was produced in 2012. This document, Document 9871, lays out the in-depth information for each level of compliance.

2.2.4.1. Within ICAO Document 9871, which features up through RTCA 260B, is the same alert priorities as 260A. For a far more in depth look also see Table B-2-97.

Surveillance Status Coding
0 = no condition information
1 = permanent alert (emergency condition)
2 = temporary alert (change in Mode A identity code other than emergency condition
3 = SPI condition

Codes 1 and 2 take precedence over code 3.

ICAO Document 9871 Figure C-1

2.2.4.2. Within Annex 10 vol IV are the details of how squawking would be initiated or rescinded.

3.1.2.6.10.1.1 Alert. An alert condition shall be reported in the FS field if the Mode A identity code transmitted in Mode A replies and in downlink formats DF equals 5 and DF equals 21 are changed by the pilot.

3.1.2.6.10.1.1.1 Permanent alert condition. The alert condition shall be maintained if the Mode A identity code is changed to 7500, 7600 or 7700.

3.1.2.6.10.1.1.2 Temporary alert condition. The alert condition shall be temporary and shall cancel itself after TC seconds if the Mode A identity code is changed to a value other than those listed in 3.1.2.6.10.1.1.1. The TC shall be retriggered and continued for TC seconds after any change has been accepted by the transponder function.

Note 1.— This retriggering is performed to ensure that the ground interrogator obtains the desired Mode A identity code before the alert condition is cleared.

Note 2.— The value of TC is given in 3.1.2.10.3.9. 3.1.2.6.10.1.1.3 Termination of the permanent alert condition. The permanent alert condition shall be terminated and replaced by a temporary alert condition when the Mode A identity code is set to a value other than 7500, 7600 or 7700.

[…]

3.1.2.6.10.1.3 Special position identification (SPI). An equivalent of the SPI pulse shall be transmitted by Mode S transponders in the FS field and the surveillance status subfield (SSS) when manually activated. This pulse shall be transmitted for TI seconds after initiation (3.1.1.6.3, 3.1.1.7.13 and 3.1.2.8.6.3.1.1).

Note.— The value of TI is given in 3.1.2.10.3.9.

3.1.2.6.10.2 Capability reporting protocol. The data structure and content of the data link capability report registers shall be implemented in such a way that interoperability is ensured.

Note 1.— Aircraft capability is reported in special fields as defined in the following paragraphs.

2.2.4.3. Moving forward, the ICAO Global Air Navigation Plan 2016-2030 emphasizes some of the important assets of the transition toward ADS-B environment. In addition to the safety aspects and improved accuracy, there is the cost of infrastructure maintenance and coverage. Within the ADS-B environment, including space based, there is the potential to provide coverage in more remote parts of the globe where only non-radar exists currently. The current systems are aging and the cost of replacing the older technology with like types is expensive whereas there could be a transition to the improved technology.

B0-ASUR (ADS-B out and MLAT), operationally, the lower costs of dependent surveillance infrastructure in comparison to conventional radars support business decisions to expand radar-equivalent service volumes and the use of radar-like separation procedures into remote or non-radar areas. Additionally, the nonmechanical nature of the ADS-B ground infrastructure allows it to be sited in locations that are difficult for radar installations. MLAT requires more ground stations than ADS-B and has larger geometric requirements than ADS-B, but has the early implementation advantage of using current aircraft equipage.

ICAO Global Air Navigation Plan 2016-2030

2.2.4.4. There is still a factor to consider in non-radar environments and their ability to practically use this information. Some parts of the world, such as Europe and the mainland United States, experience upwards of 95% radar coverage. However, this is not true everywhere. For example, there are portions of rural Australia where procedural separation is still utilized.

2.2.4.5. The need for the ability to simultaneously transmit and have SPI functions is admittedly uncommon; but there are times where this may be the sole means of communication with an aircraft. Therefore, it is important to not overlook the significance of an aircraft lacking this ability.

2.2.4.6. As technology increases around the world, areas that fall outside radar coverage should continue to decrease. This would make the ability to squawk single emergency codes even more valuable.

2.2.4.7. In many parts of the world RTCA 260B compliant equipment will be a requirement. This will lead to an increasingly valuable global network of ADS-B. As mandates for equipage that allows simultaneous squawking and SPI come into effect, the policy will need review.

2.2.5. The final portion of the policy deals with recommendations for ICAO and reads as follows, “That ICAO establishes a global position and recommendations on the management of ADS-B operations without separate emergency codes and isolated SPI function”.

2.2.5.1. In the decade since the initial paper was written ICAO has not created a global position regarding this topic.

2.2.6. Moving forward one consideration is whether ADS-B will replace other radar. If this is the case, there are concerns particularly about ADS-B being the sole replacement of surveillance in high density airspace. Risks include losing the ability to crosscheck the data from ADS-B as compared to what is seen on the radar screen and to a lesser degree ADS-B Out data lack of encryption causing potential security concerns for spoofing.

2.2.7. The second and third paragraphs could be combined into a single, more impactful statement. There is a need to keep the important portions of existing policy while also keeping an eye toward the future.

2.2.8. This would be the only remaining topic in the Surveillance section if left there. It is suggested that the Surveillance section be removed from the TPM and the remaining policy, SUR6.2, be shifted to the ATS section. The amended policy would be as follows:

Conclusions

3.1. The definitions within SUR 6.1 are still useful to IFATCA; however, the definitions should be moved to the Acronyms and Terms section.

3.2. Within 6.2 there is the need for both some minor edits and some overhaul to keep the focus on current and future needs.

3.3. Moving the former SUR 6.2 topic to ATS results in eliminating the need for the Surveillance chapter within the TPM and it should be removed.

Recommendations

4.1. It is recommended that the abovementioned sections of the Technical and Professional Manual (TPM) be amended accordingly, as described in Section 2 of this working paper.

References

Honeywell. (2019). “The Ins and Outs of the ADS-B DO-260B Compliance.” Honeywell Aerospace. https://aerospace.honeywell.com/en/news-listing/2015/october/the-ins-and-outs-of-the-ads-b-do-260b-compliance

ICAO. (2006). Document 8168 Aircraft Operations. 5th Ed. Volume I Flight Procedures. Montréal, Canada: ICAO.

ICAO. (2012). “Technical Provisions for Mode S Services and Extended Squitter.” 2nd Ed. Montréal, Canada: ICAO.

ICAO. (2014). Aeronautical Telecommunications: Annex 10 to the Convention on International Civil Aviation. 5th Ed. Montréal, Canada: ICAO.

ICAO. (2016a). Global Air Navigation Plan, 2016-2030. 5th Ed. Montréal, Canada: ICAO.

ICAO. (2016b). Procedures for Air Navigation Services – Air Traffic Management, 16th Ed. Montréal, Canada: ICAO.

IFATCA. (2019). IFATCA Technical and Professional Manual (TPM). 2019 Ed. Montréal, Canada: International Federation of Air Traffic Controllers’ Associations.

Paydar, M. (2019). “ICAO Seminar on the Implementation of Aeronautical Surveillance and Automation Systems Aeronautical Aeronautical Surveillance Surveillance and Automation Automation Systems Systems in the SAM Region.” ICAO Seminar on the Implementation of Aeronautical Surveillance and Automation Systems Aeronautical Aeronautical Surveillance Surveillance and Automation Automation Systems Systems in the SAM Region. https://www.icao.int/SAM/Documents/2010/SURAUTOSEM/03ICAO_ComparisonSurveillanceTechnology.pdf

RTCA. (s.d.) Doc 260B.

RTCA & FAA. (2019). https://www.rtca.org/content/about-us-overview

Woodrow, B. (2019). “ADS-B Security Risk Remains Unresolved for US Military.” Avionics. March 06, 2019. https://www.aviationtoday.com/2018/10/04/ads-b-security-risk-remains-unresolved-u-s-military/