BEIJING (AP) — In the sometimes-testy rivalry between Washington and Beijing, good manners count. A recent amendment to a U.S.-China accord on safe encounters between their military pilots calls for keeping a secure distance, communicating clearly and keeping a lid on rude body language.

"Military aircrew should refrain from the use of uncivil language or unfriendly physical gestures," says the third amendment to the safety memorandum.

The stipulation shows the degree to which the two sides hope to avoid unintended events, although there's no evidence that insulting behavior has been a factor in any recent encounters.

It comes as the two countries see themselves operating in ever closer contact, a consequence of China's robust assertions of its South China Sea maritime claims and a renewed U.S. focus on Asia that will see 60 percent of the Navy fleet assigned to the region.

The amendment was signed shortly before a state visit last month to Washington by Chinese President Xi Jinping, who has exerted stronger control over the armed forces than any of his predecessors since Deng Xiaoping in the late 1980s.

That came on the heels of a Sept. 15 incident in which two Chinese fighter-bombers made what the U.S. Pacific Command described as an unsafe interception of a U.S. Air Force RC-135 surveillance plane patrolling about 80 miles (130 kilometers) off the Chinese coast. Previously, a Chinese fighter jet executed a barrel-roll as it came within 9 meters (30 feet) of a U.S. Navy P-8 Poseidon surveillance plane over the South China Sea in August 2014.

In the most serious such incident, aircraft from the two countries collided over the South China Sea in 2001, killing a Chinese jet fighter pilot and forcing a heavily damaged U.S. EP-3 surveillance plane to land at a Chinese base. China interrogated and detained the 24 crew members for more than a week, sparking the biggest crisis in bilateral relations in more than a decade.

In that case, the lost Chinese pilot, Wang Wei, had previously flown close enough to U.S. aircraft for their crew to see his e-mail address written on a piece of paper held up inside his cockpit.

Within the Chinese military's "environment of bravado," the actions of rogue pilots can be hard to rein in, said Denny Roy, an expert on the Chinese military at the East-West Center in Hawaii.

However, by signing the memorandum and its annexes, China wants to indicate to the U.S. that aggressive challenges in the air are not necessarily national policy, Roy said.

"It's a positive step in bilateral relations because it indicates a Chinese interest in stability and in advancing military-to-military relations," Roy said.

Tensions have also risen over China's declaration of an air-defense identification zone over disputed islands in the East China Sea in 2013. The U.S., Japan and others have refused to recognize the move because the area encompassed by the zone includes territory controlled by Japan. China has so far made little effort at enforcing it.

Meanwhile, the South China Sea remains the area of greatest contention, with China upping the ante by building artificial islands on top of reefs and atolls it controls topped with buildings and airstrips.

Pacific Fleet Commander Adm. Scott Swift, the U.S. Navy's top commander in the Pacific, said last week his sailors were prepared to patrol within the 12-nautical mile (21-kilometers) territorial limit of the newly constructed islands. That move would reinforce Washington's refusal to recognize them as sovereign territory and assert its right to freedom of navigation.

Swift said the new amendments were potentially more significant than a formal Code for Unplanned Encounters at Sea signed by China, the U.S. and others last year.

"I'm more concerned in the air perspective because it's much more dynamic," Swift said in an interview with The Associated Press.

China's Defense Ministry welcomed the signing, with spokesman Wu Qian praising it as "of positive significance to enhancing strategic mutual trust, and avoiding misunderstanding and miscalculation."

Analysts differ, however, on how far it will go toward reducing mutual suspicion.

While the memorandum reflects Xi's control over the military, its effect on overall relations shouldn't be overestimated, said Bonnie Glaser, senior adviser for Asia at the Center for Strategic and International Studies in Washington, D.C.

"Xi doesn't want an accidental collision on his watch," Glaser said. "I think the memorandum on safety in the air and at sea can create greater predictability, but it is not likely to build trust."

Associated Press reporter Audrey McAvoy contributed to this report from Pearl Harbor, Hawaii.