The US Federal Aviation Administration had objected to the restrictive visibility of the visor used on the first two prototype Concordes, which had been designed before a suitable high-temperature window glass had become available, and thus requiring alteration before the FAA would permit Concorde to serve US airports. This led to the redesigned visor used on the production and the four pre-production aircraft (101, 102, 201, and 202).[154] The nose window and visor glass, needed to endure temperatures in excess of 100 °C (210 °F) at supersonic flight, were developed by Triplex.[155]