that's almost certainly not where the flight started, due to intricacies of how this sort of flight tracking works.

if you look at [0] it has tracks of both flights. toggle the right-hand sidebar, if it's not open already, and you'll see a table containing both planes. the helicopter (PAT25) is yellow, the plane (JIA5342) is blue. the legend right below that explains the color-coding - the plane's data came from ADS-B, while the helicopter's data came from multilateration (MLAT).

MLAT [1, 2] works by having multiple ADS-B feeder stations cooperate in real-time and deduce an aircraft's position based on timestamps of when the signal is received. it allows tracking aircraft that only broadcast the more limited Mode S data, instead of the newer and more detailed ADS-B.

because it requires multiple cooperating receivers, the start of the track in suburban McLean does not mean it took off from there. it just means that was the point in its flight where it became visible to enough receivers that MLAT was able to pin down a position.

you can also see this difference just by looking at the tracks - the plane is broadcasting its own position continuously, so its track is nice and smooth. meanwhile the helicopter's flight looks "jagged" in a way that does not match what its actual flight path would have been. this is an artifact of the small errors introduced by MLAT.

0: https://globe.adsbexchange.com/?icao=ae313d,a97753

1: https://www.flightaware.com/adsb/mlat/

2: https://adsbx.discourse.group/t/multilateration-mlat-how-it-...