SAN FRANCISCO—The Asiana Airlines jet that crashed while landing at San Francisco International Airport, killing two Chinese teenagers and injuring 182 others, was descending at a dangerously slow speed and pilots apparently ran out of time to correct their approach, investigators said Sunday. 
 
 While stopping short of pinpointing pilot error as the likely cause of the fiery crash Saturday, National Transportation Safety Board Chairman Deborah Hersman's comments indicated investigators were focused primarily on why the cockpit crew allowed speed to decay to such an extent—and failed to take decisive action until the Boeing 777 was less than two seconds from impact. 
 
 The overnight flight from Seoul, with 307 people on board, including 16 crew members, hit a rocky sea wall, which sheared off its tail and landing gear, then slammed onto the runway, skidded, spun off the tarmac and erupted into flames. 
 
 Some passengers and witnesses said it looked as if the aircraft was too close to San Francisco Bay as it approached the runway. 
 
 "There was no feeling of anything wrong. No announcement. Then suddenly the plane went bam, bam, bam, bam," said Fawen Yan, a 48-year-old resident of the San Francisco Bay area who was sitting in economy class. 
 
 Remarkably, 123 passengers walked away without major injuries after exiting from emergency slides or leaping from gaping holes in the burned body of the plane. 
 
 China's Ministry of Education said 70 of those aboard were Chinese students or their teachers bound for U.S. precollege exchange programs. Among them, according to Asiana and Chinese officials, were Wang Linjia and Ye Mengyuan, who were killed in the crash. 
 
 In the first on-scene briefing by the NTSB, Ms. Hersman said a preliminary readout of the plane's flight-data and cockpit-voice recorders indicated that everything was normal—with no discussion of any onboard problems or concerns about the visual approach in good weather—until just seven seconds before impact. 
 
 At that point, she told reporters, the cockpit crew realized the plane was flying too slowly. "The speed was significantly below" the designated approach speed of roughly 160 miles per hour. 
 
 Three seconds later, a stall-warning activated in the cockpit, indicating the jet was losing aerodynamic lift, Ms. Hersman said. The crew didn't act to sharply increase engine thrust and try to climb away from the runway—conducting what is called a "go-around"—until 1.5 seconds before impact, she said. 
 
 The safety board believes "the engines appear to respond normally" to those commands, Ms. Hersman said, but by then it was too late to recover and portions of the lumbering jet slammed into the sea wall in front of the strip. 
 
 Ms. Hersman stressed that there was "no prior distress call" from the cockpit crew, which should have been able to rely on both ground-based and onboard landing aids to "establish an approach path" to safely reach the beginning of the runway. 
 
 Since the jet was on a visual approach in excellent weather, "you don't need instruments to get into the airport" safely," Ms. Hersman said. 
 
 In another significant disclosure, she said investigators "haven't identified any specific similarities" between Saturday's crash and the 2008 belly landing of another Boeing 777, operated by British Airways, on final approach to London's Heathrow International Airport. Investigators determined the British jet's engines were starved of fuel after chunks of ice blocked its fuel system. Nobody was injured, but the incident prompted changes to the 777's fuel systems. 
 
 Taken together, the preliminary data and Ms. Hersman's early description strongly suggest investigators are leaning away from mechanical or other system failures as the likely culprit. 
 
 A young co-pilot with significantly less experience than the captain of the aircraft was at the controls of the Boeing 777 when it crashed, according to people familiar with the situation. 
 
 The co-pilot was following a routine visual approach. None of the pilots radioed flight controllers about any onboard problems or declared an emergency, according to preliminary reports. 
 
 There were four pilots in the cockpit during the approach: the captain, co-pilot, a "relief pilot" and a fourth pilot, who may not have been on duty at the time. None of the pilots sustained any significant injuries, said people familiar with the situation. 
 
 After spending the night at the airport, the pilots checked into a San Francisco hotel Sunday. NTSB and Korean investigators tentatively scheduled interviews with the crew for Monday. 
 
 The last major U.S. air accident occurred in 2009, when a Bombardier Dash-8 Q400 flown by regional carrier Colgan Air crashed on approach to Buffalo Niagara International Airport, killing 50 people. 
 
 At a news conference in Seoul midafternoon Sunday, Asiana President Yoon Young-doo and a group of executives bowed in apology. Mr. Yoon called the accident "regretful." 
 
 The airline doesn't believe the accident was caused by an engine or mechanical problem, Mr. Yoon said, but added that all facts related to the investigation would be announced by the NTSB. Mr. Yoon also said the pilots on the flight were veterans with around 10,000 hours of flying time each. 
 
 One issue likely to come under review is the overall experience and hand-flying skills of the pilots, who couldn't rely on all elements of an airport instrument-landing system as a backstop. Since last month, pilots landing at the busy airport have been warned that one type of approach aid has been temporarily turned off while work is under way to improve the strip. Alternate ground-based aids were functioning as the Asiana jet descended with both engines on idle. 
 
 In the cockpit, according to investigators and industry safety experts, there also should have been alerts if a landing plane is descending too quickly or its trajectory threatens to take it short of the runway threshold. 
 
 If onboard flight-control and speed management systems were working normally as the safety board suggests, then "guidance was available to the crew" about an approach that was becoming dangerously slow and low, said safety consultant John Cox, a former airline pilot and accident investigator. 
 
 While visual approaches typically don't require any assistance from instrument-landing systems, safety experts said some airlines prefer to have pilots rely on them as an additional safeguard under nearly all circumstances. 
 
 Investigators also are expected to examine if pilot fatigue or flight-control problems contributed to the accident, and whether air-traffic control instructions may have been a factor. 
 
 The aircraft should have been flying roughly 100 or 150 feet above the airport's surface when its tires or tail apparently smacked into a stretch of the sea wall and the jet began breaking apart, experts said. Large pieces of the tail section and scrape marks were visible near the sea wall, and both left and right portions of the landing gear were found hundreds of yards away from the main wreckage. 
 
 Despite the Asiana jet losing both left and right landing gear, its rear bulkhead, portions of the wings and at least one engine, early reports indicated that the crew and airport emergency officials quickly evacuated most passengers, before an intense fire melted its aluminum skin and left a giant gash in the top half of the middle of the fuselage. 
 
 The Boeing 777 has had a nearly unblemished record, and previously was among a small group of long-range jets from Boeing and Airbus to have never sustained a fatality in passenger service. 
 
 —William Harless, Jason Dean, Cassandra Sweet, Jon Ostrower, Alastair Gale, Kanga Kong and Liyan Qi 
 
 contributed to this article. 
 
 Printed in The Wall Street Journal, page A1 
 
 A version of this article appeared July 7, 2013, on page A1 in the U.S. edition of The Wall Street Journal, with the headline: Pilot Error Examined in Crash. ||||| Search and rescue officials surround an Asiana Airlines Boeing 777 plane after it crashed while landing at San Francisco International Airport in California on July 6, 2013. 
 
 SEOUL Asiana Airlines Inc said the pilot in charge of landing the Boeing 777 that crash-landed at San Francisco's airport on Saturday was training for the long-range plane and that it was his first flight to the airport with the jet. 
 
 "It was Lee Kang-kook's maiden flight to the airport with the jet... He was in training. Even a veteran gets training (for a new jet)," a spokeswoman for Asiana Airlines said on Monday. 
 
 The plane was travelling "significantly below" its intended speed and its crew tried to abort the landing just seconds before it hit the seawall in front of the runway, the U.S. National Transportation Safety Board said on Sunday. 
 
 "He has a lot of experience and previously flown to San Francisco on different planes including the B747... and he was assisted by another pilot who has more experience with the 777," the spokeswoman said. 
 
 Lee, who started his career at Asiana as an intern in 1994, has 9,793 hours of flying experience, but only 43 hours with the Boeing 777 jet. 
 
 Co-pilot Lee Jeong-min, who has 3,220 hours of flying experience with the Boeing 777 and a total of 12,387 hours of flying experience, was helping Lee Kang-kook in the landing, the spokeswoman said. 
 
 National Transportation Safety Board Chairwoman Deborah Hersman said Sunday that it was too early to say whether pilot error or mechanical failure were to blame. 
 
 But she said there was no evidence of problems with the flight or the landing until 7 seconds before impact, when the crew tried to increase the plane's speed and the plane responded normally. The control tower was not alerted to any plane issues. 
 
 Witnesses said the plane on Saturday appeared to be too low as it approached the runway, hit the ground before the runway started and the impact sheared off part of the tail of the plane and possibly landing gear as well. 
 
 Asiana's chief executive said on Saturday that he did not believe the fatal crash was caused by mechanical failure, although the carrier refused to be drawn on whether the fault laid with pilot error. 
 
 (Reporting by Hyunjoo Jin; Editing by Ryan Woo)
– The pilot in Saturday's plane crash in San Francisco was a veteran with almost 10,000 hours of flying experience—but just 43 of them were in a Boeing 777 and the disaster that killed two people and injured 182 others was his first attempt to land that type of aircraft at the site. Asiana Airlines pilot Lee Kang-kook was still in training for the jet and was being assisted by a co-pilot with more than 3,000 hours of flight experience with the 777, Reuters reports. National Transportation Safety Board investigators haven't settled on pilot error as the cause of the crash but the investigation is focusing on why the plane came in to land at "significantly below" the right speed and why the crew didn't try to abort the landing until 1.5 seconds before the crash, the Wall Street Journal reports. The airline's chief executive says he does not believe the crash—the first fatal one involving a 777—was caused by mechanical failure.