Junead Khan, 25, of Marlow Avenue in Luton, downloaded a bomb-making recipe and browsed the internet for a knife used by British militant "Jihadi John".
He was jailed for life in May for preparing a terror act.
This has now been replaced with a 20-year jail term with five years on licence.
The Appeal Court heard Khan opened the bomb pack computer file "only once" and, although he looked for a knife, he never placed an order.
Although he went close to US military bases in East Anglia, including RAF Mildenhall in Suffolk, he never deviated from his planned route.
"There is no doubt about the heinous nature of the crime, which Junead Khan formed an intention to commit," the judge said.
"In terms of steps actually taken, he did not carry his intention far."
He had committed a serious crime but not one that needed a life sentence, the panel of judges including Lord Justice Treacy and Mr Justice Leggatt, concluded.
The judges also dismissed an appeal by Khan and his uncle Shazib Khan, 24, also of Marlow Avenue in Luton, against their sentences of seven-years jail, with five years of extended licence, for preparing terrorism offences.
The pair had planned throughout 2014 and 2015 to travel to Syria to live under the so-called Islamic State regime, but failed to raise enough money for the fare and to buy all the kit their IS contacts had asked them to bring.
A delivery driver jailed for life for plotting to kill US personnel outside an air base has had a new sentence imposed by the Appeal Court.