A Taiwanese engineering company employee has been extradited to America on charges he sought to purchase a specialized helmet that allows fighter pilots to aim missiles by moving their heads.

So far it’s unclear whether the allegations speak of attempted espionage or merely the efforts of a Taiwaenese man with a penchant for eBay bidding to expand a personal collection of military gadgetry.

Prosecutors have noted in court papers that the man, Yen Ching Peng, works for a firm that reverse engineers military technology. But the charges he faces so far deal only with allegations that he sought to violate American export controls on military technology. He is not accused of attempting to reproduce any equipment.

Defense attorneys for Mr. Peng, who is in his early 30s, say he is simply a collector.

“He has a ‘Top Gun’-type collection,” one of his lawyers, David Katz, said, referring to the iconic film about fighter pilots.

Mr. Peng was arrested in Hong Kong last year, extradited on Saturday, and arraigned yesterday in U.S. District Court in Manhattan.

The case grew out of a sting operation that began when Mr. Peng sent an e-mail message seeking help finding “special toys” to an address operated by undercover agents for the Immigration and Customs Enforcement. Over several months, the agents built their case by selling several rifle-mounted, infrared aiming devices and thermal sites to Mr. Peng and shipping them to Taiwan, according to court papers filed by the prosecution.

Export of these optical devices, which are produced for military or law enforcement use, are tightly regulated, according to court papers. At Mr. Peng’s request, the agents would label them as “plastic toys” on export forms to avoid scrutiny, according to court papers.

For a period of months, Mr. Peng and the undercover agent corresponded about a fighter jet helmet, known as a Joint Helmet Mounted Cueing System, which allows fighter pilots to direct a plane’s weaponry to targets by pointing their heads at enemy aircraft, according to court documents. There are tight export controls on the product, although a California firm that produces the helmet at issue, Vision Systems International, is permitted by the State Department to sell the helmets to at least 10 other countries, a source with knowledge of the export controls and the company’s orders said. Taiwan is not on the list, the source said.

On December 6, 2006, an undercover agent went to a Manhattan post office to deliver the jet helmet to Mr. Peng’s emissary, a flight attendant for Continental Airlines, according to court papers.

The emissary, Peter Liu, knew Mr. Peng only because he’d allowed Mr. Peng, for a fee of a few dollars, to use his eBay account to purchase various military gadgetry, which Liu would receive and send to Taiwan, according to court papers.

Liu was subsequently arrested before he had shipped the jet helmet. A Taiwanese-born American citizen from Queens, Liu was sentenced last week to 30 months in prison.

The source questioned the value of the helmet alone, noting that it was no simple matter to integrate the helmet into the avionics of a specific aircraft.

Taiwan is currently one of the largest purchasers of American military equipment. It recently allocated the funds to purchase more than 60 F-16 fighter jets from America, although the deal has not yet gone through, a professor at Smith College who closely follows Taiwanese-American relations, Steven Goldstein, said.

“Does Taiwan want jet-plane technology? Yes, very badly.” Mr. Goldstein said, speaking generally and not about Mr. Peng’s case.

Lawyers for Mr. Peng might cite America’s close relationship with Taiwan to argue that this isn’t likely a case of espionage.

“Taiwan is supported by the U.S. and can get whatever they want,” another lawyer for Mr. Peng, Vincent Lin, said. “They don’t need to buy it from eBay.”

Mr. Lin said the division of the engineering firm for which Mr. Peng worked does not deal with military equipment.