In its rush to prove the business case for airlines to buy and use next-generation air transportation system (NextGen) avionics, the FAA faces a quandary: What happens if trials designed to show positive results reveal the opposite?

An answer could come this summer when the agency closes out a demonstration program in the South Pacific for an automatic dependent surveillance-broadcast (ADS-B) “In” application known as in-trail procedures (ITP).

ITP uses an ADS-B “Out” position, rate and identification data from nearby aircraft to indicate to pilots whether climbs or descents will be possible based on horizontal and vertical separation from other aircraft in cruise flight, particularly in oceanic areas. The idea is that if pilots are aware of potential options they will be more likely to contact air traffic control via data link to ask for a more optimal cruise altitude, typically based on winds.

With the ADS-B “In” equipment, which typically involves ADS-B “Out” data processing in the aircraft's traffic-alert and collision-avoidance system computer and a pilot interface device, either on the panel or in an installed electronic flight bag (EFB), the FAA will allow an airliner to fly 20 nm or less behind or ahead of other traffic, down from the usual 80 nm in-trail distance for Pacific routes. The ITP software will also let pilots see opportunities to climb or descend through flight levels occupied by other aircraft.

The FAA last year teamed with air navigation service providers in Australia and New Zealand to offer ITP to appropriately equipped aircraft. To hedge its bets, the agency also paid for an ITP certification effort with Honeywell, UTC Aerospace Systems and United Airlines to outfit 12 Boeing 747-400s (shown) on routes from California to New Zealand. The ITP applications are run on a Honeywell TPA-100B traffic computer with the right-side pilot interfacing with the software using a window-mounted UTC EFB.

“We've seen estimated fuel savings of $100,000-400,000 per year, but this test is the truth model,” says Scott Miller, product line director for Honeywell. “It will validate the fuel savings and look at the benefits of ITP.”

The test was supposed to begin in August 2011, but delays pushed the start to summer 2012. With 1.5 years on the books, some preliminary results revealed by the FAA fall short of an endorsement.

According to a snapshot presented by the FAA at a Jan. 14 meeting held by the General Aviation Manufacturers Association, only 2-6% of the pilots of aircraft capable of making ITP requests to air traffic control actually did so in November 2013. In the August-November period, there were 34 ITP requests from 900 ITP-capable aircraft, but only two ITP maneuvers were performed. Nine were denied. Along with the 12 United 747s, Airbus A330 and A340 aircraft outfitted with the airframer's airborne traffic situation awareness systems also can participate. Average in-trail distances from August through November averaged about 30 nm, compared to the 18-nm minimum the FAA had expected. Pilots that performed ITP climbs reported wake turbulence encounters 2% of the time, with a turbulence severity level of 5 (minimal).

One likely reason for the low uptake in the trials could be that aircraft for oceanic routes now are regularly delivered with navigation systems that qualify for 4-nm required navigation performance (RNP) capability, which allows for 30-nm in-trail separation when requested by pilots and approved by air traffic control. “Airlines have [RNP 4] equipment today,” says Miller. “They don't have to install an EFB, [traffic computer] upgrade and ITP.”

The downside of RNP 4 is that the pilots do not gain the ADS-B “In” benefit of situational awareness—seeing the leading and trailing traffic rather than relying on air traffic control to assess the situation when asking for an altitude change. That capability did help a United crew flying from London to San Francisco in November to save 1,157 lb. of fuel after requesting a “non-ITP” climb of 1,000 ft. The aircraft was taking part in a Eurocontrol ITP pilot program. Though the climb was not the result of an ITP request, United says ADS-B “In”-equipped aircraft and application of Honeywell SmartTraffic ITP gave the crew the situational awareness it needed to make the climb request.

United tells Aviation Week the London-to-San Francisco fuel savings figure is the only data it can share on its ITP trials until the final report is released, but the airline sees a silver lining from South Pacific routes.

“We are convinced that similar and much larger benefits are being accrued by ADS-B 'In'-equipped aircraft in the Pacific,” United says.