A safety assessment on a planned cable car has been launched over concerns the transport link could be too close to London City Airport.
Transport for London (TfL) has instructed the National Air Traffic Services (NATS) to conduct the review.
The cable car would link 2012 Olympic venues at Greenwich to the Royal Docks in east London.
TfL said it still aimed to deliver the project in time for the Olympics.
The cable car plan was designed to cut journey times between the O2 arena and the ExCel exhibition centre, both of which will host events at the games.
The charity Friends of the Earth wrote to London Mayor Boris Johnson concerned that the cars would travel through the "public safety zone" around the airport.
A Mayor of London spokesman said: "The mayor has received letters suggesting that further safety analysis of the cable car application be carried out in relation to the expansion of City Airport."
Friends of the Earth London campaigner Jenny Bates said: "We welcome the news that a safety assessment on the proposed cable car development has now been commissioned.
"A cable car would create a great, environmentally-friendly river crossing but the safety of the route is currently jeopardised by City Airport expansion plans."
Transport for London said: "We do not expect this process to have any material impact our planned delivery timetable.
"However this is subject to planning permission and funding being secured."
London City Airport, Greenwich and Newham councils are yet to comment.