United Continental Holdings Inc. is stepping up training and in-flight monitoring of pilots in response to a number of serious, previously identified safety lapses.

Howard Attarian, senior vice president of flight operations, laid out the carrier's plans -- and the justification for dramatic action -- in remarks to an industry conference here earlier this week. In the company's most specific comments yet on the subject, Mr. Attarian said United later this year intends to put a group of specially trained observers in selected cockpits to document the extent of pilot adherence to mandatory procedures.

Airlines, including United, have commonly relief on so-called line operations safety audits to examine pilot compliance with specific flying practices.

The airline also plans to boost training aimed at helping captains and co-pilots work more closely together as a team during flights. Mr. Attarian said officials are developing the business case to support such enhanced training modules.

The moves were prompted by a January memo to all pilots, first reported by The Wall Street Journal, that raised "significant safety concerns" prompted by four separate "safety events and near misses" in previous weeks, including one in which pilots had to execute an emergency pull-up maneuver to avoid crashing into the ground. Another flight cited in the document landed with less than the mandatory-minimum fuel reserves.

The two-page memo, signed by Mr. Attarian and the airline's top safety official, didn't provide specifics about the close calls, and Mr. Attarian didn't disclose additional details in his speech. But the January memo's unusually blunt language focused on the dangers of lax discipline and poor cockpit communication and coordination.

"You have to confront this head on," Mr. Attarian told an international gathering of airline officials and training providers. "I will not let United and our pilots operate in an unfettered, undisciplined and noncompliant manner," he added.

In the past, Mr. Attarian said, United succeeded in reducing safety hazards by relying on a combination of flight-data analysis and voluntary incident reports by pilots. Such efforts helped allay risks including those from takeoff rolls halted at high speeds, as well as near midair collision incidents.

Another company safety official told the conference that similar data analysis over the years helped reduce the frequency of pilots continuing risky approaches, in which planes were descending too quickly toward the runway or lining up to land at excessive forward speed. Results included "four consecutive year-over-year improvements" in the rate of so-called unstablized approaches, according to Chris Sharber, a United training captain.

In his remarks, Mr. Attarian stressed that the company's management remained convinced that putting out the memo was the right move, and he said the decision was supported by "most everybody" including pilots.

None of the incidents cited in the memo resulted in aircraft damage or injuries, but it underscored broader safety concerns stemming from demographic trends and personnel shifts affecting pilots, including retirements, new hires and aviators transferring to different aircraft types. Such change, according to the document, "introduces significant risk to the operation."

In his remarks this week, Mr. Attarian said "we observed behavior that was unacceptable, in my opinion." The importance of doing something to curb such lapses, he said, was "fully supported by the data" company officials analyzed. He said the training and cockpit-monitoring changes are intended to ensure that pilots operate appropriately and under "scrutiny of programs that were intended to keep the airline safe."