Strange Smell Forces Southwest Boeing 737 Diversion

Yesterday, a Southwest flight from Baltimore to Los Angeles was forced to land shortly after departure, due to the presence of a strange odor on board. Passengers were transferred to an alternative aircraft to continue their journey to Los Angeles.

A Southwest Airlines Boeing 737 NG
Flight N8507C was diverted due to an unusual smell. Photo: Bill Abbott via Flickr

The Aviation Herald reported yesterday on an incident involving an unusual odor aboard Southwest flight WN-1395. The odor was reported shortly after takeoff, causing the crew to stop their climb at around 4,000 feet.

The aircraft, a 2.9-year-old Boeing 737 NG registered N8507C, then returned to Baltimore, landing on runway 10 approximately 10 minutes after takeoff. Upon arrival at Baltimore, a visual assessment of the aircraft showed no signs of damage.

The 125 passengers onboard were then transferred to a replacement aircraft which landed in Los Angeles 90 minutes after the scheduled arrival time.

Possible causes

While the precise source of the strange odor aboard yesterday’s Southwest flight is unclear, similar incidents are surprisingly common. Unidentified ‘strange odors’ can be the result of any number of different things.

In some cases smoke in the cabin forces aircraft to land. A fire on board an aircraft can obviously be a very serious issue.

A Transavia Airlines Boeing 737
The man onboard the Transavia flight caught a deadly infection whilst on holiday. Photo: Aero Icarus via Flickr

Of course, bad odor on planes is not always a problem with the aircraft itself. In May 2018, a Transavia Airlines flight from the Canary Islands to the Netherlands was forced to divert to Portugal due to an unusually smelly passenger. The 58-year-old Russian man was escorted off the flight because other passengers found his smell unbearable.

But this incident wasn’t just a result of bad personal hygiene. The man had actually contracted an infection on holiday which started to cause tissue necrosis, and he, unfortunately, died shortly afterward.

The characteristic smell

Smelly passengers are rare, but many flights are canceled as a result of ‘unknown smells’. In these cases, the smell is often described as something akin to ‘dirty socks’ or ‘wet dog’. While it may sound unpleasant but not cause enough to divert a flight, the characteristic ‘dirty socks’ smell is actually often linked to jet engine bleed air.

When jet engine bleed air comes into contact with high-temperature engine oil, it can create dangerous toxic fumes. Usually, the jet engine bleed air and engine oil don’t come into contact, but when engine seals deteriorate, they can mix and cause fumes.

A Southwest Airlines Boeing 737-700
Jet engine bleed air can be toxic. Photo: Bill Abbott via Flickr

If these fumes hang around in the cabin for too long, they can make passengers and crew ill. Often the smell will dissipate as the aircraft ascends, but typically air crew will land as a safety precaution.

The description of a ‘strange odor’ in yesterday’s incident sounds similar to the characteristic odor of jet engine bleed air. It would also explain the crew’s decision to land the aircraft as soon as possible and the fact that no external signs of damage were detected.

Southwest Airlines’ quick response

Despite the delay caused by the unscheduled landing, the passengers aboard flight WN-1395 arrived in Los Angeles just 90 minutes behind schedule. Compared to other incidents where flights have to land due to aircraft issues, this delay time is reasonably impressive.

Unfortunately, Southwest Airlines was not available to respond to Simple Flying’s request for comment on the incident.