In brief: Having an excess of undelivered stock can cause issues, especially when the product in question is a passenger aircraft. That's the problem facing Boeing, which has so many grounded 737 Max jets that it's been forced to park them in an employee lot.

Back in October last year, 189 passengers were killed when Lion Air flight 610 crashed into the Java Sea 12 minutes after takeoff. Four months later, Ethiopian Airlines flight 302 crashed six minutes after takeoff, killing 157 people. Both are believed to have been caused by the 737's new Manoeuvering Characteristics Augmentation System (MCAS).

Following the March crash, the 737 Max was grounded worldwide while it awaited a software fix and approval from aviation authorities to restart flights.

With Boeing continuing to produce the 737 Max series jetliners but customers unable to take them, finding places to store the aircraft hasn't been easy. Seattle news station KING-TV reported that a Boeing factory in Renton, Washington, is keeping the planes next to employees' vehicles in the company parking lot.

According to Bloomberg, Boeing is storing 500 grounded 737 Max jets around the world, including 100 at the Renton factory, at a cost of $2,000 per month for each plane. Boeing said the situation has already cost it $1 billion, with inventory costs predicted to reach $12 billion by September. It's not clear when, or if, the planes will ever return to the skies.

"We're going to bring a Max back up in the air that will be one of the safest airplanes ever to fly," Boeing CEO Dennis Muilenburg told reporters. "But we also know it will take time rebuilding the confidence of our customers and the flying public, and this will be a long-term effort."