A spate of aviation incidents over the past few days is raising fresh safety concerns in the wake of January's near-catastrophe involving a Boeing 737 MAX.

Why it matters: Many travelers are on edge heading into the busy summer air travel season.

Driving the news: A United Airlines Boeing 737 MAX 8 slid off the runway while landing in Houston Friday morning. It's unclear if mechanical issues played a role, though news footage suggests the landing gear collapsed at some point.

• "We are closely monitoring the situation and will provide any support needed to United Airlines and the investigators," a Boeing spokesperson tells Axios.

A day earlier, a United Boeing 777 lost a tire shortly after takeoff from San Francisco. The aircraft landed safely in Los Angeles and nobody was injured, though the flying tire smashed into a parked car.

• Large aircraft have multiple wheels below each wing, and can land safely if some are damaged or missing.

On Monday, a United Boeing 737-900 safely returned to Houston after flames were spotted spewing from one of its engines, which had "ingested some plastic bubble wrap that was on the airfield prior to departure," the airline says.

• Safety regulators are also investigating a February episode in which the pilots of a United 737-800 experienced stuck rudder pedals after landing in Newark, the National Transportation Safety Board said Thursday. The related parts have already been replaced on the affected aircraft, United says.

The big picture: Each of these incidents will be investigated separately. Based on what's currently known, there's nothing to suggest a link between them — despite the fact that they all involved United-flown, Boeing-made aircraft.

• While aircraft manufacturers are responsible for assuring they build and deliver safe planes, airlines are chiefly on the hook for maintaining them post-delivery.
• Engines, meanwhile, are made separately from the aircraft they propel, and by different companies.

Our thought bubble: Aircraft are highly complex machines, and minor-to-moderate mechanical issues aren't uncommon — especially given that there's tens of thousands of passenger flights globally on any given day.

• To some extent, what's happening here may be chalked up to "frequency illusion" — we're paying extra attention to aviation mishaps because we're all at least a little freaked out about January's 737 MAX door blowout.

Yes, but: That's not to minimize any of these incidents, which all deserve investigators' attention, as they may turn up useful information for aircraft makers, operators and travelers.