Flight Crew Air Transport Pilot (ATP)
Conflict NMAC
General None Reported / Taken
Airspace Structure
We were in cruise flight at FL400. The weather was clear VMC. My Captain stated 'what's that' and pointed to the right side of the aircraft; 1 o'clock position; same altitude. I leaned forward and looked past the window post between the R1 and R2 windows. I noticed a white balloon moving in our direction. I stated that it was in sight and that it looks like we are going to miss it. The balloon passed our right wing seconds later. I noticed a white balloon with a small box attached to it by a cord. It was close enough for me to see the cord swaying back and forth. It is difficult to say how many feet it missed us by but I can say that it was close enough to see it in detail as we quickly flew passed it. The event last seconds from the time it was spotted. Washington center was notified immediately afterwards. Upon landing we reviewed the required reports section of the Flight manual and determined that a report was required. If my Captain had not been looking in that location at that exact time we probably would not have noticed it due to the color; size; and closure rate.
While at FL400 cruise near/over ROA; I spotted a white weather balloon floating towards the aircraft. (No TCAS alerts) It was at our altitude and we could clearly see the tether hanging down from the balloon that supported a small silver instrument package. The instrument package was hanging slightly below our altitude. The best I could determine; the balloon appeared to be perfectly round in shape. Since nothing was near it; I am not able to determine the actual size of the balloon. The balloon passed off our right wing tip closer than 200 ft and may have been as close as 100 ft.I reported the balloon to Washington ARTCC immediately and they acknowledged my report. Nothing more was mentioned about the incident by ARTCC.If the balloon's instrument package had carried a transponder that reported altitude and course (drift); ATC could have alerted me to the proximity of a balloon and used vectoring to avoid hitting the balloon package. At 400+ kts ground speed; if the tether had hit the wing or if the instrument package had impacted the cockpit or had been whipped around to hit the fuselage; we could be talking about a rapid decompression; damage to hull or wing and possibly loss of life.
B737 flight crew reported an NMAC with a weather balloon at FL400 over Virginia.