The Release of Dropsondes: A Hazard for Commercial Air Traffic?

This paper addresses the question of the probability with which meteorological sondes dropped from aircraft would collide with other aircraft flying at lower levels. Real air traffic data for Germany regarding the total number of aircraft and the fleet composition are used for the calculations. An overall collision probability of about 2.6*10-6 is estimated for a randomly and uncontrolled dropped sonde to collide with an aircraft, considering peak traffic density. From this probability one collision would statistically be expected out of about 386,000 drops. In reality the release of dropsondes is supervised by the Air Traffic Control Authorities, reducing the risk to very nearly zero in controlled airspaces. A certain risk will remain for sondes dropped in any airspace without radar surveillance, such as the North Atlantic Flight Corridor. But even this risk could be minimized by specific control procedures. In all, the risk is much less, about 1/4, of that which currently exists in the case of upsondes released on balloons from the ground. These largely uncontrolled upsondes or radiosondes, as commonly termed, penetrate the airspace levels used by commercial air traffic.