RAAS to the rescue?

Air Safety Week, Oct 18, 2004

The pilots of a Northwest Airlines A319 with 122 passengers who mistakenly landed June 19 on a U.S. Air Force base instead of their nearby destination commercial airfield were fired about a month later (see ASW, June 28). The two airfields, Ellsworth AFB and Rapid City airport, are about seven miles apart, the Rapid City field being described as "just over the hill" from Ellsworth and the crew was descending through clouds. Details of the case have been the subject of recent coverage by the Pioneer Press newspaper of St. Paul, Minn. The paper obtained copies of the air traffic control tapes, in which surprised Air Force watch standers remarked that the base commander was going to be "a little upset" over the unexpected landing of the commercial jetliner on the B-1 bomber base.

The two pilots were replaced by another crew, who flew the A319 the few miles to its correct destination about three hours after the inadvertent landing.

The incident pilots have filed a grievance against Northwest for terminating their employment.

There are a number of interesting aspects of the case:

* Was this incident the culmination of precursor events? There are reports of several previous instances of pilot confusion between Ellsworth AFB and Rapid City Airport.

* How'd the crew lose situational awareness? Descending toward Rapid City, the flight crew was flying a VOR (very high frequency omnidirectional range) approach, intended to guide them to the general vicinity of the runway. Apparently, when they broke out of the clouds, they sighted what they believed was Rapid City's Runway 32, pushed the nose over (suggesting an unstabilized approach) and mistakenly landed on Ellsworth's Runway 31. With all the high-tech navigation equipment with which their A319 was equipped, including GPS and moving map displays, the crew still landed on the wrong runway, at the wrong airport.

* What did the air traffic controller advise? In cases of airports in close proximity, aren't controllers supposed to say, "Northwest 319 Ellsworth Air Force Base is at your 11:00, Rapid City Regional is at your 12:00. Report Rapid City Regional in sight." At least, that is the kind of guidance that should have been radioed, according to Federal Aviation Administration procedures (FAAO 7110.65), Chapter 7, Section 4 on visual approaches, subparagraph 7-4-3g, which says, "In those instances where airports are located in close proximity, also provide the location of the airport that may cause the confusion."

The hypothetical question that comes to mind is whether the incident pilots would have been sufficiently alerted if the Honeywell [HON] Runway Awareness Advisory System (RAAS) had been fitted to their airplane. In addition to its pre-takeoff and after-landing advisory messages, the system is designed to aurally advise pilots of the runway on which they are about to land when the airplane is some three nautical miles distant and within or - 20 degrees of the runway centerline (see ASW, June 16, 2003). A typical voice advisory would be, "Approaching two-five." In cases where two runways are within or - 20 degrees heading of each other, then the message "Approaching runways" is generated.

In this case, the pilots mistakenly landed on Ellsworth's runway 31. Their intended touchdown was at Rapid City's runway 32. According to Honeywell officials, their systems database for RAAS and the Enhanced Ground Proximity Warning System (EGPWS) is "enabled" for Rapid City. However, the database for Ellsworth is enabled for EGPWS only. The incident airplane was equipped with EGPWS.

What this all means is that even if the incident airplane had been equipped with RAAS, it would not have issued an advisory that the pilots were approaching Ellsworth's runway 31. They would have heard the standard altitude callouts from EGPWS, which might have subtly reinforced their belief that they were landing at Rapid City. (For more on RAAS and EGPWS, see http://www.egpws.com/raas/raas.html)

Approaching Runway - RAAS In Air Advisories

RAAS equipped aircraft provide the flight crew with an aural advisory when the aircraft is airborne and approaching a runway. This advisory is enabled when:

* The aircraft is between 750 feet and 300 feet above the airport field elevation (AFE), and

* The aircraft is within approximately three nautical miles of the runway, and

* The aircraft track is aligned with the runway within or - 20 degrees, and

* The aircraft position is within approximately 250 feet, plus runway width, of the runway centerline.

All EGPWS aurals have priority over this RAAS advisory. The "Approaching Runway - In Air Advisory" is suppressed between 550 feet and 450 feet above runway elevation to allow normal 500-foot altitude call outs and/or crew procedures without conflict. If the advisory is triggered while the aircraft is between 550 and 450 feet above field elevation (AFE), the advisory is suppressed until the aircraft descends below 450 feet AFE, where the message will be annunciated.

If the criteria above are not satisfied before the aircraft descends below 300 feet AFE, the advisory is aborted.