ICAO Document #4444, PANS-Air Traffic Management is the primary guidance for published contingency procedures when operating in Oceanic or Remote Continental airspace. These published contingencies allow you to safely deviate from your assigned clearance, in the event a revised clearance cannot first be obtained.
The procedures are designed to rapidly separate you from the regular flow of traffic while you address an emergency. Not every possible emergency or contingency can be proceduralized and explained. The most common cases that might require a pilot to fly oceanic contingency procedure without an ATC clearance include:
- Unexpected meteorological conditions
- Engine Failure
- Cabin Pressurization Failure
- Loss of Communications
- Loss of navigation capability
- Significant reduction in navigation capability
- Medical Divert Situations
When in training, typically only the classic textbook examples are explained or even demonstrated in a simulator. Almost never does deviating for cause without an ATC happen in a textbook environment. These contingency procedures can tremendously increase in risk if a poorly executed contingency is in play or if the prescribed procedure is not employed when off your ATC clearance’s assigned route, altitude and speed. The reality is pilots need do some pre-flight strategy and operational cockpit briefing before the immediate need for a contingency develops unexpectedly.
One Contingency Does Not Fit All
For this discussion we are going to concentrate on the “General Oceanic” contingency procedure published in ICAO Document #4444, Paragraph 15.2 and the “Emergency Descent” inside Paragraph 15.1.4
Worldwide the “General Oceanic” procedure results in a 45˚ turn off course and a 15 NM lateral offset. The altitude change happens at 10nm (if you are able to maintain altitude) and is 500’ different from those normally used inside of RVSM (FL290-FL410) and 1,000 feet outside of RVSM. This procedure has direct application across the Pacific region, the Indian Ocean and most of the rest of the world.
One difference inside ICAO Doc#4444 that you may notice right away, is when you compare this “General Oceanic” to the “The Weather Deviation” procedure found in Paragraph 15.2.3. The Weather Deviation” procedure results in an altitude change of 300 feet, when the lateral deviation exceeds 10 NM from centerline. So there is our first departure from the standard, 500’ vs. 300’ and 15nm vs. 10nm.
Another example of contingency differences in found in the People's Republic of China (Mainland China). The PRC lists no difference to these procedures inside their AIP. This is in contrast to the published procedure by the PRC that uses 30˚ for the turn off course and always to the right of course. The PRC requires the use of SI units of measure and lists 20km as the final distance for the offset course.
NAT HLA Differences
There are significant revisions to the current ICAO Doc #4444 Paragraph 15.2 “General Oceanic” Contingency Procedures that are applicable inside NAT HLA and the New York FIR. This revised procedures plus a revised “Weather Deviation” procedure were included in the current edition of NAT Doc#007 published in March 2019. The expectation is that these revisions will be adopted into a future revision of ICAO Doc#4444.
For operations inside the NAT HLA region and the New York FIR, offset distance used inside the General Oceanic contingency and Weather Deviation contingency have been reduced to 5NM. The 500ft altitude split (in RVSM) for General Oceanic remains the same as does the 300ft offset for the Weather Deviation procedure. This new procedure also differs from the ICAO Doc#4444 in that 30˚ course offset is used vice the standard 45˚.
The NAT planners have restated a strong recommendation for pilots to consider a descent below FL 290 where there is a predominant traffic flow or parallel Organized Track System, OTS if the aircraft’s diversion path will likely cross adjacent tracks or routes. Descent below FL 290, and establishing as required by the operational situation is the preferred procedures vice deviating across an OTS at 500’ offset altitude. Altimetry system errors may lead to less than actual 500ft vertical separation when the crossing an OTS and needless ACAS RAs may occur.
Emergency Descent Thru an Organized Track System
The procedural differences we have discussed so far are well published and operationally straightforward for pilots to employ in the NAT HLA. But what about a “Random Route” above the OTS with a required descent thru the tracks below that distress aircraft? This is requires a higher level of understanding and procedural compliance. To find the procedure required for a descent thru an OTS, pilots will have to dig into ICAO Doc#7030. This recommended procedure is not listed in Doc#4444, or in NAT Doc#007. It is referenced in AC 91-70B but not explained.
A distressed aircraft needing to make a descent through NAT HLA airspace and an OTS, (whether diverting off track, continuing to destination or turning back) should plan to descend to a level below FL 280. Prior to passing FL 410, proceed to a point midway between a convenient pair of organized tracks and while descending between FL 410 and FL 280, maintain a track that is midway between and parallel with the organized tracks.
This is the requirement BUT how to comply? Electronic monitoring of own-ship’s position is a terrific tool for this. A plotting chart and updated position prior to descent is the next best thing. Of course leaving the ACAS/TCAS on and using an outside scan to pick up traffic visually will round out the risk mitigations.
The ACAS II Overview from EASA contains a recommendation to limit the TCAS/ACAS to “TA-Only” when in an emergency descent. This would result in an “RA” for conflicting aircraft while in an Emergency descent but only a “TA” for the distressed aircraft. Similar recommendations can be found in AC 120-55 and ICAO Doc#8168, PANS-Ops, Volume 3, Chapter 3, Paragraph 3.1.
Inside ICAO Doc#4444, Paragraph 126.96.36.199 is a procedure for all pilots hearing a distress call from an emergency descent aircraft. Unless specifically instructed by ATC to clear the area or if threatened by immediate danger, pilots are expected to continue according to current clearance and maintain listening watch on the frequency in use (HF or CPDLC and 121.5/123.45) for any further instructions from ATC and keep watch for conflicting traffic both visually and by reference to ACAS.
Random Routes May Not Really Be “Random”
There is a poor habit that says, “If I’m on a Random Route, I don’t hafta’ worry about the Tracks”. This is a load of…. nonsense. Use of the NAT OTS tracks is not mandatory, this much is true. It is just good planning and part of the due diligence for pilots to know where expected traffic is when operating Oceanic/Remote. Aircraft may flight plan on random routes that remain clear of the OTS or may fly on any route that joins, leaves, or crosses the OTS. During the hours of validity of the OTS, operators are permitted to flight plan along a route to join or leave an outer track of the OTS or on a route to remain clear of the OTS, either laterally or vertically. The NAT HLA specifically requires that operators have a copy of the NAT Track message on-board for operations. A best practice is to compare your current ATC clearance to the current published track message and look for similarities in routing and altitudes. It is possible for a “Random Route” to mirror image an OTS routing at an unpublished altitude.
Pacific operations require specific planning for User Preferred Routes, UPR to remain clear of the NOPAC and PACOTS routing. There are no such margins required from random UPR to other UPR routes except for ATC separation standards. Currently “30/30” separation is the common standard however, with PBCS this is being reduced to as little as 14nm.
1. Not every contingency situation will be covered by ICAO Doc#4444.
2. Regional Supplements found in ICAO Doc#7030 can be hard to find.
3. Guidance material such as NAT Doc#007 is good place to start a study.
4. Random Routes are not always set apart from Organized Track Systems.
5. With tighter separations in Oceanic/Remote airspace the margin for error in a contingency execution are narrower.