A Southwest Airlines Boeing 737-800 flying from San Diego to Indianapolis was forced to divert to Las Vegas on Thursday after a recurring maintenance indication. Flight WN651, carrying 141 passengers and crew, notified air traffic control of the persistent issue before requesting a diversion as a precaution.

The 737-800 landed safely in Las Vegas, with the crew reporting that they had « run out of cooling » before requesting emergency services. The airline deployed a replacement Boeing 737 MAX 8, which flew the passengers onward to Indianapolis at a delay of around three hours.

Southwest 737 Diverts After Maintenance Indication

As reported by the Aviation Herald, the Southwest Boeing 737-800 (registered as N8513F) was en route to Indianapolis when the pilots requested a diversion to Harry Reid International Airport (LAS), citing an indication in the cockpit. As the aircraft was on approach to LAS, the pilots requested to cancel their approach and enter a holding pattern, as the indication had stopped but then reoccurred, necessitating another run of checklists.

ATC responded that it had declared an emergency for the aircraft, which landed safely on Runway 26L approximately 45 minutes after reporting the issue. As the aircraft was taxiing to the gate, the pilots informed ATC that they had run out of cooling before requesting an inspection by emergency services for smoke or hot spots. Simple Flying has reached out to Southwest Airlines for comment and will update this story accordingly.

The Boeing 737 Involved: N8513F

Flight WN651 on Thursday was operated by a nine-year-old Boeing 737-800 delivered to Southwest in December 2016. Per data from ch-aviation, the aircraft has accumulated over 30,000 flight hours and 15,000 flight cycles during its time in service at Southwest.

The 737-800 can accommodate up to 175 passengers in an all-economy cabin, with Southwest operating almost 200 examples of this 737NG variant. The low-cost carrier has been operating the 737-800 for over 13 years, taking delivery of its first aircraft in March 2012. Southwest used one of its Boeing 737 MAX 8 aircraft to operate a replacement flight for passengers out of Las Vegas. This flight arrived in Indianapolis just before midnight, representing a delay for passengers of around three hours.

In the end, it was quite a fast turnaround for the affected passengers, with Southwest able to quickly call upon a replacement plane at its busy Las Vegas base. The airline is the dominant carrier at LAS with over 40% of the market, flying to over 70 destinations. The 737 MAX 8 is the second most numerous aircraft type in Southwest’s fleet at almost 300 planes, closing in on its 737-700 fleet, which consists of just over 310 aircraft.

Precautionary Diversions

It is not uncommon for aircraft to divert to the nearest suitable airport due to an indication in the cockpit, even for apparently minor issues. In each event, pilots are required to run through a checklist before opting for the safest course of action, which will often be to discontinue the flight and divert as soon as possible.

The flight crew’s report that the aircraft had run out of coolant suggests a problem with its equipment cooling or environmental control systems, which poses a serious enough threat to safety to necessitate an immediate diversion. Indications related to the aircraft overheating can have potentially catastrophic consequences, which is why emergency services were called for by the flight crew.

Limited information about this incident is available at this stage, so the extent of the aircraft’s problem is unclear. Data from Flightradar24 shows that N8513F was returned to service the next day, operating Flight WN1863 from Las Vegas to Denver (DEN) in the morning before another flight to St Louis (STL) in the afternoon.