Marine One came within 0.82 nautical miles of a passenger jet—but still met the applicable separation rule

On Aug. 4, Marine One and a departing Envoy Air E-170 came within 0.82 nautical miles laterally—0.94 miles—and about 700 feet vertically. The applicable Class B rule required either 1.5 nautical miles laterally or 500 feet vertically, not both, so the 700-foot gap satisfied the minimum. The concern was the coordination failure: a presidential-departure procedure called for a three-minute warning so the tower could stop DCA takeoffs, but the tower never received it and cleared the jet as Marine One lifted off. The jet’s collision-avoidance system issued a traffic advisory, though no avoidance command followed. Open ADS-B data recorded the Envoy jet at roughly 143–150 knots near the reported incident location. At that ground speed, it travels 0.82 nautical miles in about 20–21 seconds and one regular mile in about 21–22 seconds. That describes the jet’s travel speed, not the rate at which the aircraft were approaching each other: the NTSB says the traffic target remained to the jet’s right and below, then passed behind it. The NTSB calls this a “loss of separation event” while also saying the applicable radar minimum was met. Marine One’s first warning call was not received, its second was unreadable, and a backup relay failed.