ADS-B”€”Hope Or Hype?

The FAA has been taking the position that only certified equipment can be installed on aircraft with standard airworthiness certificates. The FAA is also exploring the possibility of setting standards for battery-powered ADS-B Out transmitters that can be used on gliders and general aviation aircraft certificated without an electrical system. Additionally, the FAA is working with the aviation community to set standards for how ADS-B In provides pilots with a low-cost traffic alerting capability. The FAA says that aircraft owners or avionics shops may install an uncertified GPS on an amateur-built aircraft with an experimental airworthiness certificate. Uncertified GPS units don't meet the equipment requirements associated with the mandate and don't qualify for ATC services using ADS-B data. Data from aircraft with uncertified GPS units aren't displayed on certified ADS-B In displays, and pilots of aircraft with certified ADS-B equipment won't be able to see aircraft equipped with uncertified GPS units.

The aviation alphabet groups have been pushing for a way to sharply reduce the cost of equipping to meet the FAA's 2020 mandate. One argument is that tens of thousands of aircraft owners will give up flying rather than spend an estimated 25% of their airplane's value on ADS-B equipment.

Transitioning to ADS-B isn't going to be merely a matter of throwing a switch or two. Training is going to be required in using the electronic boxes, as well as interpreting and using the information that's provided while understanding its limitations. Already, the NTSB's accident files are beginning to contain evidence that the conversion to ADS-B may not be the safety panacea that's being promised.

Mooney M20M
Both the pilot and passenger on board a Mooney M20M were killed when the airplane impacted terrain in Crane Hill, Ala., on September 17, 2012. The airplane was on an IFR flight plan in instrument meteorological conditions. It took off from Destin-Fort Walton Beach Airport (DTS), Destin, Fla., and was on the way to Sumner County Regional Airport (M33), Gallatin, Tenn.

According to air traffic control information provided by the FAA, the airplane departed DTS at 12:45 p.m., and was subsequently issued a heading of 330 degrees and a climb to 10,000 feet. At 12:53, the pilot was told to switch to Jacksonville Center and to expect vectors around a weather cell from the Center controller. At 12:54, the pilot made contact with the next controller and reported out of 7,000 for 10,000 feet. The controller advised the pilot of "extreme" precipitation and asked his intentions. The pilot stated that he was looking at "ADS-B" weather. The controller then told the pilot to maintain 13,000 feet and approved deviations left or right of course, and to proceed direct to destination when able.

At 1 p.m., the controller asked the pilot to state his flight conditions, which the pilot responded were cloudy and smooth, with light rain becoming heavy, and that the ride was a "little bit bouncy." Two minutes later, the controller made a general broadcast to all aircraft on the frequency that convective SIGMETs were available. At 1:06, the controller handed off the flight to Atlanta Center.

At 1:17, the pilot asked the Atlanta controller if there were any reports of icing up ahead at 15,000 feet. The controller responded that there were no reports of icing, "but quite a bit of deviation, quite a bit of clouds and precipitation in front of you." The pilot requested 15,000 feet "to see if I can see things better," which was approved by the controller.

At 1:25, the pilot was told to contact the center's next sector controller. When the pilot came up on the next frequency, the controller advised him of moderate to extreme precipitation for about the next 90 miles along the route of flight. The pilot subsequently stated that, in looking at the ADS-B, he needed to deviate about "three five eight degrees for several miles and probably head back north again." The controller approved 10 degrees right and left deviation, proceed direct to Sumner County Airport when able. The pilot said that he was turning to 358 degrees.

At 1:34, the controller advised the pilot of moderate to extreme precipitation at his 12 o'clock position, mostly off to his right, about 12 miles ahead. The pilot requested another 10 degrees deviation to the left, and the controller approved deviations left and right, and direct to the airport when able. The pilot advised he was turning to a new heading of 320.

At 1:54, the controller told the pilot to change to a new frequency, and the pilot radioed back, "Unable, we're battling some pretty bad..." (End of transmission.)

Plotted radar data indicated the airplane made a number of heading and altitude changes. At 1:59:06, the pilot radioed "Mayday," followed a few seconds later by additional Mayday calls.

A witness stated that at the time of the accident, it was raining "like crazy," but with no thunder. He heard an engine noise; it "sounded like he had power, then [he] heard a 'thud.'" When the witness arrived at the accident site, the airplane's cabin was on fire.

Before departure that morning, the pilot contacted flight service for a weather briefing. The briefer advised of a line of thunderstorms and another area of rain with lower IMC, and an additional line of thunderstorms tracking toward the pilot's destination. The briefer also noted a convective SIGMET with small clusters of convection moving north, and from the Alabama-Tennessee border to the destination was a large area of embedded convective activity that didn't look like it was going to dissipate anytime soon. The briefer then provided some suggested routing, but noted that because the flight wasn't leaving for an hour, the temperature would get warmer, and the convective area would expand in coverage and intensity.

The pilot then asked about icing because the airplane would be at 13,000 feet, and it wasn't approved for flight in known icing. The briefer advised that there was an AIRMET out for icing between 13,000 and 25,000 feet, but didn't indicate the area covered.

A bit later, the pilot again contacted flight service to file a flight plan. The briefer provided a weather update that included mention of an area of thunderstorms "moving toward your route of flight," and IFR conditions from northern Alabama to the destination.

The NTSB studied weather radar images that would have been available to the pilot via his ADS-B equipment. Because of a time lag between generation of the original images and processing of the data for transmission, what the ADS-B would be showing wasn't a true picture of the actual weather conditions. Pilots have been warned in an NTSB Safety Alert that NEXRAD mosaic radar images may be 20 minutes or more behind what actually is going on. In this accident investigation, the NTSB stated that there were "significant differences in depiction of hazardous reflectivity values" between actual conditions and what the pilot was seeing in the cockpit on the ADS-B equipment.

In addition to the time delay of the weather images, there was another issue that might have made it difficult for the pilot to see the whole weather picture. Although he held a third-class medical certificate, he had in the past failed the color vision portion of the eye examination and was unable to distinguish between red and green. Those are among the colors used in the display of different levels of weather radar reflectivity. He held a Statement of Demonstrated Ability for the color vision issue.

The NTSB determined that the probable cause of the accident was the pilot's loss of control in moderate to heavy rain. Contributing to the accident was the pilot's reliance on ADS-B for tactical weather avoidance.

In its Safety Alert on NEXRAD weather radar mosaic images, the NTSB pointed out that, "Even small time differences between the age indicator [on the cockpit display] and actual conditions can be important for safety of flight, especially when considering fast-moving weather hazards, quickly developing weather scenarios and/or fast moving aircraft. The in-cockpit NEXRAD display depicts where the weather was, not where it is."

In the Aeronautical Information Manual, the FAA warns that weather images such as provided through ADS-B "...are not appropriate for tactical avoidance of severe weather such as negotiating a path through a weather hazard area." The FAA says they should only be used for strategic decision making such as route selection to avoid a weather hazard area in its entirety. The FAA warns, "The misuse of information beyond its applicability may place the pilot and aircraft in jeopardy." That's one of the many things pilots will need to apply in understanding the benefits and limitations of the ADS-B system.

Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other news concerning the National Transportation Safety Board. To subscribe, write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, N.Y. 10602-0831.