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(as published in Pro Pilot Magazine, Outer Marker Inbound, January 2007) A Time and Place for SLOP-y Navigation
By Roger Rose Some skies were actually safer prior to 1994. The inherent inaccuracy of INS equipment, born of drift rates, induced a separation that enhanced safety. I recall my first GPS crossing in amazement. I had “gone to bed” near Gander and returned to my JetStar’s cockpit at about 20W, and witnessed a stack of four contrails above, all within the lateral displacement of a hundred feet or so.
In those days, our new lateral navigation capability relegated the INS to seemingly pre-Columbian standards. We were amazed by the collinear contrails and pleased that navigation could be so cheap, dependable and precise anywhere on the planet. A mere four years later, a harbinger of the flip side of such accuracy occurred off the southwest coast of Africa.
Its literal impact seemed little acknowledged outside of Africa.
A Luftwaffe TU-154 was cruising southeasterly at a non-standard altitude and out of contact with ATC. They apparently elected to remain at the last assigned altitude and not to monitor or use the regional IALPA In Flight Broadcast Procedure (IFBP, frequency 126.9).
For those pilots unfamiliar with African ops, the IFPB was implemented as a specialized position broadcast, inclusive of airway and direction of flight. For participating crews, it effectively bridged the gaps in a region where inter-FIR communications were not consistent and where bi-lingual control denigrates the situational awareness of crews unable to function in multiple languages.
Concurrently, a US Air Force C141 was cruising northwesterly at the same altitude, as cleared by the sector he was last working. The Air Force crew was using the IFBP although the Luftwaffe TU-154 crew neither received the C141’s reports nor broadcast their own position.
With these scant few gaps, the dual marvels of GPS lateral accuracy and RVSM vertical accuracy delivered these aircraft radome to radome at close to a thousand knots. It was likely not a lengthy outcome.
Out of self preservation, I immediately implemented and recommended offsets anytime that ATC integrity was compromised. Sometimes the compromise was structural, as in some of the “Foxtrot” airways that have now all but disappeared from the African continent. Such airways sported an “F” suffix that indicated the “Foxtrot” Category of airspace (uncontrolled) usually due to inadequate ATC services – advisory rather than controlling.
My offsets were always within the containment value of the applicable airspace, meaning less than one nautical mile laterally (always to the right). The logic was to offset to the right and hope I didn’t run into a Brit driving up the left side of his or her “road”. Hence, the addition of a vertical offset in Africa, of 30 meters (100’), to further ensure that we miss a diligently driven radome, wing-tip or tail.
In the last year, the London based NAT’s office implemented SLOP--Standard Lateral Offset Procedure for the North Atlantic Organized Track System (OTS). It was thought by many to be optional and primarily for wake turbulence. SLOP gave crews the choice of flying course centerline, 1 nm or 2nm offset and always to the right.
At the 2006 Tampa NBAA International Operators Conference, a NATs presentation made us acutely aware that SLOP is mandatory when operating in conjunction with the OTS (Organized Track System). More importantly, they underscored that it was necessary “in order to return the Target Levels of Safety” to this heavily trafficked Class II airspace.
This included a detailed narrative on the natural dispersion of aircraft in the pre-GPS oceanic structure—a tacit acknowledgement that extreme levels of accuracy in the absence of full ATC facilities (or crew situational awareness) can be a bad or even fatal combination.
Last month’s mid-air collision between a Legacy and a Boeing 737, over Brazil, will take months to unravel and sadly, the case is currently being tried in the blinding glare of an uninformed press. It is true that 154 lives were ended and many more were forever changed.
To me, it appears that the recent collision differed in merely superficial ways and should serve as the “canary in our coal mine”. It occurred in Class I but remote airspace and the element of language may have removed key information from some of the participants. Lastly, the safety nets of TCAS and ATC collision avoidance measures still failed to separate the two aircraft.
Whatever the cause(s), one truth is abundantly evident to me. Technology is not a panacea. Unless accompanied by an overlay of sensible human factors, reason and luck, technology may only solve one problem while creating another potentiality.
So now that the dirty little secret is out (again), what is there to do about it?
In the inevitable time that it takes for ICAO and national bodies to overcome inertia, perhaps crews should implement a SLOP-y offset of .1 to .7 nm. That equates to 600-4200 feet. It should be sufficient to miss that radome, tip or tail and yet ensure the accuracy intended by regulators and considerably more than was safely delivered by VOR’s or INS’s.
Leave the crews in charge of its implementation. Perhaps the best cue is when that little voice tells you that you may not have the entire traffic scenario available to you. That trigger might be multi-lingual control or a standard of altimetry with which you are not so familiar—although we apply only lateral offsets in metric altimetry environments.
Given the glacial pace of regulatory change and now the second mid-air collision in less than a decade, with similar causes, what would you do?
About the Author
Roger Rose, is an IBAC accredited safety auditor and past Chairman of NBAA’s International Ops Committee. More than half of his thirteen thousand hours has been logged in the Gulfstream family of aircraft (G1 through G550). He has operated internationally since 1973, living sixteen years outside the US, holding full licensure in four countries and validations in another nine. He has been published in a number of aviation and maritime journals from Aviation International News and ProPilot Magazine to Lloyds List and the Marine Log.
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Last Updated ( Thursday, 23 October 2008 )
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