The first of the National Transportation Safety Board’s three days of investigative hearings is underway to help determine what caused the deadly midair collision on January 29 between an Army helicopter on a training mission and American Airlines flight 5342 landing at Ronald Reagan Washington National Airport.
The helicopter route at the time of the collision allowed the Black Hawk to fly as close as 75 feet below planes descending to land on runway 33 at Reagan National Airport, according to the NTSB. With allowable errors in the helicopter’s altimeters and other equipment as well as Army rules expecting aviators to hold their altitude within 100 feet, it could end up being much closer.
“How much tolerance should we have for aviation safety whenever civilian lives are at risk?” asked Todd Inman, NTSB board member. “How much is that tolerance,” he continued. “I think it should be zero.”
Sounds like the tolerances weren’t big enough! Odd interaction putting those two paragraphs next to each other. NTSB demanding zero margin for safety…
Not zero margin, zero tolerance in the margin. Very different things. If you have a margin of error of 200, and each side has a tolerance of 100, both can be technically in tolerance but still collide. You want that margin to be larger than the tolerances combined, plus additional margin for human error and real world conditions. And then, if possible, double or triple that.
The altitude systems being able to be 100 feet off while at low altitude and a separation of 75 feet is absolutely insane.
Right. I know my friend in civil engineering plans bridges as if they have 18 wheelers stacked end to end, fully loaded across the bridge, and then doubles that number. I think he’s mentioned other types of projects use safety margins of three or five multiples.
Sounds like the tolerances weren’t big enough! Odd interaction putting those two paragraphs next to each other. NTSB demanding zero margin for safety…
Not zero margin, zero tolerance in the margin. Very different things. If you have a margin of error of 200, and each side has a tolerance of 100, both can be technically in tolerance but still collide. You want that margin to be larger than the tolerances combined, plus additional margin for human error and real world conditions. And then, if possible, double or triple that.
The altitude systems being able to be 100 feet off while at low altitude and a separation of 75 feet is absolutely insane.
Right. I know my friend in civil engineering plans bridges as if they have 18 wheelers stacked end to end, fully loaded across the bridge, and then doubles that number. I think he’s mentioned other types of projects use safety margins of three or five multiples.