UPDATE 1-GKN's aerospace trading 'disappointing', faces external claims

(Adds profit forecast, quote)

LONDON, Oct 13 (Reuters) - British engineering group GKN said full-year profit would come in lower than expected due to "disappointing" trading in aerospace in the third quarter and two external claims that were expected to cost 40 million pounds ($53 million).

The company said it now expected its full-year pretax profit to be "slightly above" the 678 million pounds recorded in 2016. Analysts on average had forecast profit to rise to 735 million pounds, according to Thomson Reuters data.

"Trading in the third quarter has been disappointing with a significant reduction in margin caused by on-going pricing pressure, continuing operational challenges and the impact of programme transitions," it said of its aerospace operations.

It said the headwinds would not ease in the final quarter.

Chief Executive Nigel Stein also said recent margin performance had not met his expectations.

"In addition, it is disappointing that we expect to have to provide for two unexpected claims which will slow our steady growth in profits," he said.

GKN did not disclose details about the external claims, one of which is in aerospace and one in its Driveline automotive power transmission business, saying they were commercially sensitive.

The company said Driveline was continuing to outperform a global market growing at around 2 percent, but it was having to bear additional costs for raw materials and investment in systems for electric vehicles. ($1 = 0.7535 pounds) (Reporting by Paul Sandle; editing by Kate Holton)