That headline is supposed to make you wonder what ADS-B is, as I did the first time I read about it. The mid-air collision, of course, is the tragedy that happened last January 29 when American Airlines flight 5342 from Wichita, Kansas, was coming in for its final approach to runway 33 of Ronald Reagan Washington National Airport. About half a mile from the end of the runway, the plane collided with a Black Hawk helicopter. Both aircraft crashed into the Potomac, killing all 64 on board the airliner and the three crew members on the helicopter. It was the worst U. S. air disaster in terms of fatalities in over twenty years, and the U. S. National Transportation Safety Board (NTSB) is continuing its investigation following a briefing held Feb. 6 for members of Congress.
As reported in a piece from CNN, NTSB chair Jennifer Homendy said at the briefing that it was not clear whether a system called ADS-B in the helicopter was working at the time of the crash. The critical nature of this question becomes clear when we realize that the height of the helicopter at the time of the crash is something that hasn't yet been explained.
Airliners coming in for a landing have to follow a definite glide path in order to reach the runway, and so there are strict restrictions on where other aircraft can go near airports as busy as the Reagan National. The Black Hawk helicopter was flying something called Route 4, and was practicing what are called "government continuity operations." In other words, if the President and other key government figures have to get out of town in a hurry, they are going to travel by Black Hawk helicopter, and the people flying the helicopters have to keep in practice.
Presumably, the routes flown by these helicopters are height-restricted so planes approaching the airport will pass above the helicopters. Whether the Black Hawk involved in the mid-air collision was too high is a critical question, which is where ADS-B comes in.
That acronym stands for Automatic Dependent Surveillance—Broadcast, and it is a souped-up version of the transponders that commercial aircraft have had for years which tells air-traffic controllers what height a plane is flying. And that system was a step up from the old follow-the-blips technology that traffic controllers had to use in the early days of radar-assisted air traffic. Knowing how high an aircraft is helps a controller decide whether two converging blips just mean a harmless intersection of two flight paths at different altitudes, a scary near-miss, or a disaster like the one that happened last month.
When fully operational, an ADS-B unit in the Black Hawk would have updated air traffic controllers every second with a GPS-determined three-dimensional location data burst. This is vastly superior to what the controllers' radar can tell them on its own. And knowing that the helicopter was high enough to collide with the American Airlines plane would have at least allowed the controllers to alert the pilots to the problem.
That is exactly what happened only a day before, when an air traffic controller warned an Embraer ERJ 175 to abort a landing at a different runway at Reagan National because a nearby helicopter was flying at 300 feet. Although there appeared to be enough altitude difference between the two aircraft, the controller alerted the passenger plane's pilot anyway, who flew around and landed successfully later. Whether the helicopter in this incident was a Black Hawk or something else is not clear from published reports. But near-misses like this can provide warning flags for safety-conscious operators, who can apply lessons learned and prevent major disasters such as the one that happened January 29.
Late last week, crews successfully recovered all the major pieces of both aircraft involved in the accident, and the hope is that among the rubble is information about whether the helicopter's ADS-B system was working, malfunctioning, or turned off. The signal that ADS-B transmits is readable by anybody, so in an actual emergency flight carrying the President to parts unknown, it's likely that the system might be turned off for security reasons. In peacetime it's fine to announce your exact location to all and sundry, but in a combat situation it's the last thing you want to do.
The bottom line on this accident remains to be discovered, as we still don't have critical questions answered such as the one about the ADS-B system. Speaking statistically, if one decided to stage a mid-air collision, one would have quite a challenge, because the volume of air occupied by a Black Hawk is not that large, and exquisite timing and aiming would be required. Unfortunately, the statistics were not favorable on that deadly evening.
According to a Wikipedia article on the ADS-B, the U. S. somewhat lags behind other countries in requiring adoption of the system by most aircraft. I suspect it is a fairly costly piece of avionics, involving data links to a plane's GPS system and a 1-GHz-range microwave transceiver and antenna. Both aircraft were definitely equipped with ADS-B, but as mentioned above, it has not been determined whether the Black Hawk's unit was operational at the time of the crash.
More generally, this incident provides a good reason to speed up the adoption of ADS-B, which provides faster and more accurate data to air traffic controllers, who need all the help they can get. Another issue unearthed at this early point in the investigation is that the control office in charge of the airspace was understaffed at the time, and one controller was handling situations normally dealt with by two individuals. Whether this understaffing contributed materially to the collision remains to be seen, but the Federal Aviation Administration, which oversees air traffic control operations, is not exactly a poster child for governmental efficiency. Other countries such as Canada have transformed their FAA equivalents into private non-profit organizations, paying for them by user fees, and sometimes this makes things run better and cheaper. But that is an argument for another day.
We will keep an eye on the investigation of Flight 5342's crash, and hope that lessons learned will be applied to keep anything like this from happening again.
Sources: I referred to an ABC News article on the ADS-B question at https://6abc.com/post/washington-dc-plane-crash-major-pieces-helicopter-deadly-midair-collision-recovered-ntsb-says/15882589/, an NBC news article on the helicopter's route at https://www.nbcnews.com/news/us-news/black-hawk-helicopter-investigation-pilots-flight-path-dc-plane-crash-rcna190031, and a CNN article on the day before's near-miss at https://www.cnn.com/2025/01/30/us/dca-plane-helicopter-crash-invs/index.html, besides the Wikipedia articles on "2025 Potomac River mid-air collision" and "Automatic Dependent Surveillance—Broadcast."
P. S. This blog lost one of its most faithful and long-standing readers with the passing of David Jenkins, K4COG, on Feb. 1. I met David in 1980 at a lecture I gave at the Bible translation organization Wycliffe Bible Translators, and being fellow amateur-radio operators, we hit it off and kept in touch for the following 45 years. He will be sorely missed by his family and many friends. To Dave, I say "God bless and 73."
No comments:
Post a Comment