OSLO (Reuters) - Norway expects two F-35 fighter aircraft that were grounded for repairs last month to be back in the air by the end of November, sooner than originally thought, the defense ministry said on Wednesday.

The U.S. Air Force on Sept. 16 said 15 Lockheed Martin Corp F-35A Lightning II aircraft had been grounded due to peeling and crumbling insulation in avionics cooling lines inside the fuel tanks.

The issue affected 57 aircraft, of which 42 were still in production, it said at the time.

The insulation is now being removed and extra filters installed to intercept any potential remains, although it has not yet been decided whether this fix should be regarded as temporary or permanent, the Norwegian ministry said.

Norway plans to buy up to 52 F-35s, of which four have so far been delivered.

(Reporting by Terje Solsvik)