JAKARTA, Indonesia — After a second day of searching without any confirmed sighting of wreckage, the Indonesian authorities on Monday sought to lower expectations about finding survivors from a missing AirAsia jet carrying 162 people.

JAKARTA, Indonesia — After a second day of searching without any confirmed sighting of wreckage, the Indonesian authorities on Monday sought to lower expectations about finding survivors from a missing AirAsia jet carrying 162 people.

“We realize that we have to be prepared for the worst,” Jusuf Kalla, Indonesia’s vice president, told reporters in Surabaya, the city from which the Singapore-bound plane took off on Sunday.

Mr. Kalla said that around 30 ships and 15 aircraft from four countries had joined the search for the jet in the Java Sea, between the islands of Borneo, Java and Sumatra.

Bambang Soelistyo, the head of the National Search and Rescue Agency in Indonesia, offered even more sobering comments earlier on Monday when he said that the aircraft was probably “at the bottom of the sea” and that Indonesia lacked adequate equipment to conduct an underwater search.

Relatives of the plane’s passengers gathered in airports in Surabaya and Singapore, waiting in hopes of news.

A woman at the Surabaya airport wandered by looking stunned and bereft and holding a framed photograph of a family of five.

“They were on their way to Singapore to visit their 12-year-old daughter,” said the woman, Nani, who said she was the family’s maid. “That girl is now an orphan.”

But with officials offering few hard details, experts and some news reports were speculating on the cause of the disappearance, from bad weather to fears that the aircraft was traveling too slowly to stay airborne.

Search teams, which included fishing boats pressed into service and vessels from Malaysia, Singapore and Australia, covered a large swath of sea near the island of Belitung, the last known location of the plane, an Airbus A320-200.

Officials said the countries were working together “seamlessly,” but were hard-pressed to search underwater.

“The capability of our equipment is not optimum,” Mr. Bambang said.

Search-and-rescue teams on Monday spotted debris that turned out to be unrelated flotsam, the same kind of false alarms that plagued the search efforts for the Malaysia Airlines plane that disappeared over the Indian Ocean in March.

Planes Near Flight 8501 Around the Time It Disappeared       

Although weather was suspected as a factor in the aircraft’s disappearance, Pramintohadi Sukarno, an official at the Transportation Ministry who is helping lead the search, said background checks were being carried out on all passengers as part of standard procedures.

Some experts expressed fears that faced with stormy weather the aircraft may have been traveling at an angle and speed that would not sustain flight. This was a key factor in the crash of an Air France flight over the Atlantic Ocean in 2009, when pilots, encountering foul weather and with instruments seeming to malfunction, failed to recognize that their aircraft had entered an aerodynamic stall.

Hugh Ritchie, the Singapore-based chief executive of Aviation Consultants International, said the plane was flying at about 100 knots below general cruising speed, well within the safe envelope for flight but possibly a sign that it was climbing, had experienced severe icing or slowed to better manage turbulence.

“My personal opinion is they should not fly through this type of weather,” he said. “I think this is probably a combination of severe weather and pilot error in terms of the flight path.”

Flight 8501 was operated by the Indonesian affiliate of AirAsia, a regional budget carrier based in Malaysia. Another Malaysian jet, Malaysia Airlines Flight 370, disappeared over the Indian Ocean in March, while Malaysia Airlines Flight 17 was shot down over eastern Ukraine in July.

But the connections appeared to be nothing more than awful coincidence.

Richard L. Aboulafia, an aviation analyst at the Teal Group in the United States, said that Flight 370 “was most likely an act of human malfeasance or terrorism, while this looks for all the world like bad weather.”

Many Indonesians were frustrated at the slow pace of news and the country’s slow response to the jetliner’s disappearance.

“Many countries acted fast to help us,” said Gunawan, a travel agent who, like many Indonesians, uses only one name. “Singapore, Malaysia were fast. Indonesia wasn’t fast.”

He said one of his employees was on the flight.

The mayor of Surabaya, Tri Rismaharini, said Air Asia has been too slow providing details on the missing aircraft.

“We have lost 81 people from Surabaya with no explanation, no help,” she said. “Air Asia gave us names but that’s it.”

The Indonesian news media was investigating the life and habits of Capt. Iriyanto, quoting friends and relatives saying the captain took his family last week to visit the grave of his younger brother, who died recently. He was also described as a fan of motorcycles and a devoted member of his local mosque.

He had previously worked as a pilot at Adam Air, a troubled Indonesian airline with a disastrous safety record. Kompas newspaper quoted the pilot’s cousin saying that Captain Iriyanto moved to AirAsia after Adam Air shut down in 2008.

Adam Air epitomized a low point in Indonesian aviation. Amid a string of other mishaps and malfunctions, a Boeing 737 belonging to the airline spiraled into the sea in foul weather in 2007, killing all 102 people on board. The impact of the crash on the water was so severe that the aircraft disintegrated; the first trace of wreckage was found only 10 days after the crash.

Yet while Sunday’s disappearance is yet another blemish for Indonesia’s aviation safety record, it is not necessarily a reflection of a systemic failure at AirAsia or of the civic aviation safety system.

The airline, the leading Asian budget carrier, had carried 250 million passengers since its founding more than a decade ago without a fatal accident.

The possibility that bad weather played a role in the disappearance has renewed debate over whether pilots have access to enough data to warn them of weather-related dangers.

“The fact is there’s more technology and automated alerting on some of the apps on your smartphone than are on these planes today,” said Bob Marshall, chief executive of Earth Networks, a company that provides global weather data. “The vast majority of the world lacks adequate technology and alerting that pilots need to help keep the plane you’re flying in out of harm’s way.”

An Indonesian pilot who now works for an airline in the Middle East said pilots traversing the Indonesian archipelago are often confronted with large and potentially volatile cloud formations, especially during the monsoon season. But he doubted that more or better technology was the answer.

He flies the same series Airbus that disappeared on Sunday and said the onboard weather radar is “perfect.”

“Accidents can happen anywhere,” he said.