Germany's Lufthansa airline on Tuesday reported that it returned to profit in the first quarter despite the crash of a subsidiary's aircraft in the French Alps and six days of strikes by pilots, according to German press agency (DPA).

Net profit was 425 million euros (475 million dollars), compared with a loss of 252 million euros in the first quarter of 2014, the Cologne-based carrier said from its hub in Frankfurt.

Falling fuel prices helped put Lufthansa back in the black despite the March 24 crash of a Germanwings Airbus A320, which killed 150 people, and the strikes, which cost Lufthansa 42 million euros.

The effects of the ongoing labour dispute on Lufthansa's bottom line has rippled into the current quarter, dampening interest in bookings as customers fear further walkouts and costing Europe's biggest airline another 58 million euros, it said.

Fuel costs fell 14 per cent year-on-year to 1.3 billion euros in the first three months of the year. Also a help was a 503-million-euro gain made from Lufthansa's sale of stock in the US airline Jetblue.

Revenues rose 8 per cent to 6.97 billion euros, helped by a strong dollar.

Lufthansa still recorded an adjusted loss before earnings and taxes of 167 million euros, but the figure was down from 240 million euros a year earlier.

Despite the improved first quarter, Lufthansa warned it faces an increasing pension burden. Its pension obligations rose from the beginning of the year by 41.2 per cent to 10.2 billion euros, it said.

Pensions are at the heart of the labour dispute Lufthansa is having with its pilots.