B777 single trail question
I spend a great deal of time watching aircraft fly over my house so I am familiar with contrails and similar phenomena. I have just watched a BA B777 at around FL100 inbound to Heathrow issuing a single"contrail" from the tail. Nothing was coming from the engines. It obviously was not anything unusual as the aircraft joined the hold for Heathrow along with other traffic but I have never seen that before.
I'm sure someone knows what it was and I would be glad to know. Thanks.