UPDATE 1-Lockheed F-35 jets grounded at Luke Air Force Base -USAF

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June 9 (Reuters) - The stealthy F-35 fighter jets made by Lockheed Martin Corp have been temporarily grounded at one U.S. Air Force base because pilots were experiencing "psychological incidents," an Air Force spokesperson said on Friday.

Lockheed and its main partners Northrop Grumman Corp , United Technologies Corp's Pratt & Whitney and BAE Systems Plc have been developing and building F-35s for the U.S. military and 10 allies.

The 56th Fighter Wing at Luke Air Force Base in Arizona, canceled local flying operations for its F-35A Lightning II aircraft due to five incidents in which pilots experienced hypoxia-like symptoms. Hypoxia is often associated with oxygen deprivation.

The Air Force said the incidents first began on 2 May and during each "the aircraft's backup oxygen system operated as designed" and the jets were able to land safely.

A Lockheed representative said "our team stands ready to help in any way possible to address this issue."

The F-35 business accounted for about 37 percent of Lockheed's total revenue during the last fiscal quarter, which ended March 30.

During the quarter, Lockheed's revenue from its aeronautics business increased 8 percent to $4.11 billion, led by higher sales of the F-35.

The Pentagon said that it was conducting a comprehensive review of the facts and circumstances surrounding physiological episodes along with industry experts.

The Pentagon added that the F-35 enterprise takes a multi-disciplinary approach to monitoring and tracking physiological issues within the fleet and integrating findings to improve the weapon system and the tactics, techniques, and procedures with which it operates.

There are more than 200 F-35's deployed at air bases around the world. (Reporting by Mike Stone in Washington DC and Arunima Banerjee in Bengaluru; Editing by Arun Koyyur, Bernard Orr)