A Urban Streetlite was used, as this was a new service and the Streetlites were a interim measure until the arrival of the E200MMCs it was accepted that there was no other option.
Now the E200MMCs have been introduced, it is generally expected where ever possible 47557 is used as it is in base Flyer livery, with a different Streetlite or Dart on the A2. If this isn't possible, a Urban Streetlite will be used as a last resort.
Generally, the downtime on the E200MMCs is kept to a minimum and maintenance carried out as quickly as possible. The Streetlite will go out in the morning for several trips and then replaced with an E200MMC once complete.
This being a contract service, the choice of vehicle and livery is chosen by the customer, Bristol Airport. First have to abide by these terms as specificed in the contract.