United Airlines issues safety warning bulletin to pilots

SAN FRANCISCO -- United Airlines is warning its pilots after mistakes in the cockpit put passenger planes in potential danger. ABC News obtained a message from United officials describing four different events.

The memo, sent early last month, points out "safety events and near misses" across the industry, including a UPS plane crash in Alabama in which the crew didn't realize they were too low.

The statement also mentions two other incidents, one an emergency pull-up to avoid crashing into the ground and the other a plane landing with low fuel levels.

The memo tells pilots, "Let's not for a moment think something like that could not happen at United."

The message is clear - flight crews must be careful.

"Every pilot," it says, "must be willing to speak up if safety is in question."

Meanwhile, Southwest is back at full capacity after having to cancel about 100 flights because of overdue back-up hydraulic system inspections for nearly a third of its fleet.

"It doesn't make me feel too safe knowing they didn't keep it up to inspection and it makes me feel, 'Is my flight going to go down? Is there anything else they didn't check?'" passenger Emalee Williams said.

Industry experts say the Southwest case should give passengers comfort. "For anybody flying Southwest Airlines, I would say, don't worry about this at all. Actually it is evidence that the system is working. They found a problem, they corrected it."

The FAA worked out a deal with Southwest. They can keep flying those planes, but need to have them all inspected by Sunday.