MANILA, Philippines -- (UPDATE) The United States military has sent a spy plane and the Philippine Navy will dispatch a patrol ship and an aircraft to help in the search for two Philippine Air Force (PAF) pilots who went missing with their AS211 jet over Kalayaan Islands in the disputed Spratlys, officials said.

Fitted with state-of-the-art sensors and detection capability, the P-3C Orion was initially deployed Monday night in the Spratlys but after a futile four-hour search and bad weather caused by tropical storm “Lando” (international codename: Hagibis), the plane was forced to return initially to the Antonio Bautista Airbase in Puerto Princesa City before proceeding to Clark Air Base in Pampanga, they said.

Colonel Jose Tony E. Villarete, Wing Commander of the 570th Composite Tactical Wing, said the Air Force jet, an AS-211 reconnaissance plane, was with another AS-211 plane when it lost contact some 15 nautical miles southeast of Pag-asa Island.

Reported missing were pilots Captain Gavino Mercado Jr. and Captain Bonifacio L. Soriano III. They were following a lead plane piloted by Captain Ryan Sigin and Captain Alfred Sarmiento when they reportedly lost radio contact.

Lieutenant Colonel Epifanio Panzo, PAF spokesman, said the US spy plane resumed its search at 10:52 a.m. Tuesday but “did not find anything.”

Panzo added that a Philippine Navy islander aircraft has been placed on standby in case the spy plane finds the missing plane.

"We also asked the help of local fishermen to provide us with information on the missing jet," Panzo said.

The AS-211 can fly for a maximum of four hours with its fuel capacity,
Panzo said.

PAF Chief Lieutenant General Horacio Tolentino has also grounded all three remaining AS-211 jets as SOP (standard operating procedure),
Panzo said.

"We're still hoping to find the pilots alive. This is still a search and
rescue operation. Last night, the P-3C Orion arrived and conducted a search from 7 till 11:30 but it turned out negative and went back to Clark Air Base," Captain Alex Asuncion told reporters in a briefing Tuesday morning in Puerto Princesa City.

Meanwhile, the Philippine Navy will dispatch a patrol ship, the BRP
Rizal, to look for the PAF jet, Navy spokesman Lieutenant Colonel
Ariel Caculitan said.

"It is an unfortunate incident brought about by the typhoon… The weather was bad but our pilots had to go there to search for a missing Filipino fishing vessel," Armed Forces Chief Hermogenes Esperon Jr. said.

Reports said that the two aircraft took off from the Antonio Bautista Air Base in Puerto Princesa City at 8:45 a.m. Monday with a companion plane in response to a distress call from a Batangas-based fishing fleet that had reported 28 crewmen missing near Pag-asa during the typhoon.

The fishing fleet had 87 crewmen on board three separate vessels. One of their boats reportedly sunk in the vicinity west of Pag-asa and its
crewmen were rescued by a passing Chinese fishing vessel.

Pressed by reporters, Esperon said he was "discounting" the possibility that the AS-211 was shot down.

The oil-rich Spratlys is being claimed by the Philippines, China, Vietnam, Tawian, Brunei, and Malaysia.