BRUSSELS—The European Commission said Tuesday it has opened an in-depth antitrust investigation into United Technology Corp.’s $16.5 billion proposed purchase of Goodrich Corp. on concerns that it could undermine competition in some parts of the aviation-equipment sector, Bloomberg and the Wall Street Journal reported Tuesday.

United Technologies faces an in-depth probe by European Union regulators into its bid to buy Goodrich Corp. for $16.5 billion amid concerns the deal may harm competition for engine controls and AC power generators.

The European Commission extended its deadline to rule on the deal until Aug. 9 to examine it in greater detail, according to an e-mailed statement. The company said it remains confident the purchase will close by mid-year.

The EU’s antitrust commissioner Joaquin Almunia said, “The aviation equipment industry is already concentrated and is characterized by high barriers to entry.”

United Technologies, which has aviation brands including Pratt & Whitney engines, agreed to buy Goodrich in September, adding a maker of aircraft landing gear and jet-turbine casings to take advantage of a record surge in commercial plane orders. Goodrich employs about 700 at its aircraft wheel and brake plant in Troy.