Many flight tracking sites like Flight Aware, Plane Finder and Radar Box remove flights at the owner's request. Even ADSBExchange, which doesn't filter any flights, does not receive tracking information from most military helicopters due to the Code of Federal Regulations Title 14, Chapter I, Subchapter F rule 91.225 which makes an exemption to mandatory flight transponders for "sensitive government mission for national defense, homeland security, intelligence or law enforcement." We have found this exemption to be broadly applied to flights as innocuous as honorary funeral flyovers at Arlington Cemetery and Air Force recruiting events. This makes an enormous amount of helicopter flights over the NCR untraceable in any systematic way. As a result, we rely on user submitted photos and identification of helicopters in addition to a separate system that allows users to categorize helicopter radio calls to/from DCA tower.

All CopterSpotter reports are voluntarily submitted, and thus cannot be considered a measured random sample of the full population of like events. One thing that can be reasonably expected from Copterspotter data is that the number of reports received represents the lower measure of the true number of such events that are occurring.

A unique quality to Copterspotter data - unlike ADSB - is it inherently represents the helicopters that people notice. In other words: if a helicopter flies over a forest and no one is around to hear it, as far as CopterSpotter is concerned - it didn't happen. Another way of thinking about it: CopterSpotter is like the Nielsen ratings of DC helicopters: what helicopters D.C. residents are currently watching.

One bias we acknowledge is what we will call "rarity bias," or that someone would decline posting a medical helicopter, for example, because it is too common and does not interest them. As a spotter, you can mitigate this bias by deciding whether you will post a CopterSpotter sighting before you see or attempt to photograph the helicopter.

Luckily the DC area is uniquely positioned to benefit from CopterSpotter data because:

1. The high proportion of military and government agency flights that are not reported on ADSB

2. Operators can be reasonably inferred by aircraft type. If a user can identify type based on blades on the primary rotor, landing gear and tail shape, we can infer the operator with a high degree of accuracy.

We want researchers and residents to have access to this data so we have made an anonymized copy of the 2022 data set, after corrections were made to types based on provided images, available for download in the CSV format here. In addition, the last year of our data is browsable on The CopterSpotter Map, our computer vision model is public and it is available on the Roboflow Universe.