Easyjet said yesterday that its first-quarter revenue soared by 15% on a year ago, and predicted pre-tax profits would rise by 50% this year.

The low-cost airline said its load factor - a measure of how many seats it sold as a percentage of capacity - also improved.

EasyJet's main discount rival, Ryanair, painted a similar picture earlier this week when it said the introduction of baggage charges helped profits to rise by a 30% to 48m (£32m) in its most recent quarter, beating analysts' forecasts.

EasyJet, led by chief executive Andrew Harrison, aims to lift pre-tax profit by 40% to 50% in the year to the end of September by holding down costs and focusing on selling extras like car hire, travel insurance, excess baggage, food and priority boarding.

Last year, the group boosted pretax profit by 56% to £129m.

Investors took profits from EasyJet and the shares, which have gained 84% in the last year, fell 15p to 675p.

EasyJet said it had introduced five new routes in the first quarter of the current year, including a service between Glasgow and London Gatwick three times a day.

The group said that average fuel costs in the six months to the end of March would be 7% higher than last year at around $650 per tonne, despite a recent slide in oil prices.

Last year's first half comparatives came before oil prices soared in April to reach record levels in July.

EasyJet attacked the recent doubling of air passenger duty (APD), which raised the airport departure tax on an easyJet ticket from £5 to £10.

The airline said: "The increase in APD raises over £1bn for the chancellor but is an ineffective environmental tax.

"APD does not cover freight journeys by air and it does not differentiate between airlines in recognition of their varying efficiency and environmental credentials.

EasyJet's total revenue per seat grew 4%, with ticket sales up 2.3% and revenues from extras like food 22% higher year-on-year.

Analyst Andrew Fitchie at Collins Stewart said: "EasyJet has a solid fan club and today's upgrade and the strong earnings momentum should keep holders happy. However, we believe easyJet's valuation is now looking very stretched."

He said that on a valuation of 19 times 2007 earnings, compared to Ryanair on 18.3, easyJet should be rated hold at best. "If the shares rise too much further we would encourage investors to sell," he added. Total first-quarter group revenue was £366m.

EasyJet said its load factor was up 0.7 percentage points at 74.9% in January.

The airline said passenger numbers in January rose 11.1%.

Meanwhile, easyJet's bigger rival, British Airways, saw its share price take off after announcing it had formally agreed a plan to reduce its pension fund deficit with its unions in return for changes to benefits for employees.

The deal finalises one agreed late last year and follows a stand-off last month with its largest union in which a series of three 72-hour walkouts was narrowly averted.

"British Airways and the trustees of the New Airways Pension Scheme have formally agreed the funding plan including benefit changes to tackle the £2.1bn deficit in the scheme," the company said in a statement to the London Stock Exchange.

Meanwhile, investment bank Merrill Lynch upgraded BA's shares to buy from neutral.

In Paris, Air France-KLM, the world's biggest airline by revenue, said passenger traffic rose 2.2% in January as the company boosted capacity.