We’re all well aware of air rage that could be sparked by an airline passenger’s inability to recline their seat a few inches. 

But on Sunday, a United Airlines plane had to be diverted and two people were kicked off after they started arguing over Knee Defenders--a $22 gadget that attaches to a passenger's tray table and prevents the person in front of them from reclining. 

What are Knee Defenders? 

Knee Defenders come as a set of rubber grips that attach to the seat-back tray in front of you. About the size of a house key, the device was invented by Ira Goldman, a 6-foot-3 Washington, D.C. attorney who started selling it online in 2003 after he says was tired of getting hit in the knees when someone in front of him reclined his or her seat.  

According to the product website, the gadget is adjustable, to help provide “as much protection as you need.” 

You can also download a "Knee Defender Courtesy Card" from the site, which explains to potentially upset passengers in front that you are using the device to protect your knees. 

Are they legal? 

The gadget does not violate any FAA regulations (it can't be used during taxi, takeoff, and landing, when the tray must be upright) but individual airlines have set rules about the use of the device. All major airlines, including United Airlines, prohibit its use. For unruly passengers who do use the item, the Federal Aviation Administration can impose a civil fine of up to $25,000. In Sunday’s case, no arrest was made. 

The controversy 

The incident has brought renewed attention to the question:  is reclining your seat a right or a privilege? 

A number of low-cost airlines, including Allegiant, Spirit, and Ryanair, have already adopted what’s called “fixed recline” or “pre-reclined” economy-class seats for short-haul flights, as has Air France. 

A poll last year showed that nine out of 10 travellers want reclining seats banned - or only allowed during set times on short-haul flights. Many feel that as long as a passenger has the ability to control their seat, they have the right to recline.  

“If the airlines will not protect people from being battered, crunched, and immobilized – very real problems according to health care professionals, medical studies, government agencies, and even some airlines – then people need options to protect themselves,” Gadget Duck wrote on its website.

Politely asking your fellow passenger not to recline might be the best first option.  Some passengers have resorted to a bribe to get passengers in front of them not to recline their seats.  Whatever the strategy, the outcome could impact everyone on board.

The recent dispute on the United flight escalated to the point where the airline decided to divert to Chicago's O'Hare International Airport-- then continued on to Denver without the disorderly passengers --arriving 1 hour and 38 minutes late.