The airplane seat recline button - so controversial that it inspired an entire micro-industry of devices to stop the passenger in front leaning into your space.
At one point in time all economy class airline seats had built-in recline. Today, there are entire seat models that simply don't have the option.
So what happened to make reclining seats disappear in some places? And is that a good thing, or a bad thing? Just because a passenger can recline their seat, should they?
As with so much in the airline business, it depends on who you ask.
Let's talk about how recline works. At its most basic, there's a mechanism hidden in the structure underneath your seat cushion that contains a pivot, the wires connecting it to the button on your armrest, and a pneumatic canister that returns the seat to an upright position. Seatmakers call this kinematics: the parts that move.
For airlines, this represents a cost, firstly from maintenance: any kind of mechanism is prone to breaking, whether from normal wear and tear or because passengers don't treat airplanes gently.
Secondly, it's a weight cost, because these mechanisms can quickly add up. Most modern and lightweight airplane seats are somewhere between seven and 10kg per passenger today. Any weight that can be saved means reducing the fuel needed to carry it.
And thirdly - and in some ways most importantly - it's a disruption cost, because if passengers are fighting with each other over seat reclining etiquette, then flight attendants have to play schoolyard monitor. In some cases, passengers got so disruptive that flights have even diverted for safety.
Counting every inch
So, what if seats didn't recline?
In the late 2000s, a new generation of highly engineered super-lightweight seats started to break into the market, and part of what made them super-lightweight was that there was no recline function. Some marketing genius thought of calling them "pre-reclined," fixing the backrest at an angle somewhere between fully upright and slightly reclined.
Initially, they were mostly aimed at low-cost carriers. Usually operating flights of just a few hours, these airlines are famous for cutting all the frills out of their operation.
An early adopter was UK airline Jet2, a European package vacation company, which in 2009 chose a pre-reclined seat from then-upstart seatmaker Acro that revolutionised how airlines think about seats.
Then called Clark, and now called Series 3, Acro's seat was different in several key ways.
The lack of recline was one of them, but another was the innovative way that the seat was sculpted out of the seat pan and backrest into a fixed, concave "bucket" shape.
From behind, this shaping meant taller passengers could position their knees on either side of the "bucket,'" gaining a couple of inches of potential space.
That couple of inches really matters. There are around 30 rows of economy on an all-economy single-aisle airplane like a Boeing 737 or Airbus A320, and the previous generation of seats were spaced at around 30 inches (about 76cm) of pitch - that's the space between a point on one seat and the same point on the seat in front, so basically your space minus the thickness of the seat itself.
If an airline can save one inch of space per row, that's 30 inches across the plane, which works out to an entire extra row of seats.
Over the last decade and a bit, a variety of seatmakers have innovated around pre-reclined seats and other ways to save those inches.
One of the best regarded is German seatmaker Recaro, known outside of aviation for its racing car seats. As well as fully featured economy class seats for long-haul flights with recline and a tilting seat pan, Recaro Aircraft Seating also offers slimline pre-reclined seats for shorter flights.
The rise of the pre-recline
"The airline can choose a pre-defined backrest angle position of 15 or 18 degrees within the seat configuration process," explains Recaro's chief executive officer, Mark Hiller. "This helps to provide either more comfort via increased backrest angle or fulfil special layouts with specific passenger counts.
"The main advantage is increased living space, as a passenger's living space is not intruded by recline. In addition, the low total cost of ownership - fewer moveable parts on the seat, improved reliability and simplified maintenance - and low weight and cost, with no mechanism, kinematics and so on required."
The special layouts Hiller mentions are often what the industry calls "max pax", the maximum passenger count certified for an aircraft. That's currently 244 passengers on an all-economy Airbus A321neo narrowbody, an airplane on which some airlines with spacious business class seats up front have under 150 passengers.
It should be obvious that a 244-seater version of that airplane, or even one with 230 seats and up, is not going to be the most spacious.
But seatmakers in the last few years have figured out ways to make it feel like there's more space at your knees: thinning the seatback, moving the structure to where it's out of the way of knees, and improving the clearance for shins.
Over the last few years, the slimline seats that were previously mostly used by low-cost carriers have been finding their way onto full-service airlines as well - not least because the full-service airlines are competing directly against lower-cost competitors.
One of the ways they're doing that is by offering economy-plus extra legroom seating for sale at the front of the economy cabin, which might get a more fully featured seat model with recline and AC power sockets, while regular economy might be pre-reclined and have no power or just an USB outlet.
These are called hybrid cabins, so look out for them when you next board a plane: the colour of the seat fabric might change from row to row, the movable headrest might disappear, or the seat covering might go from fabric to leather.
So, are pre-reclined seats a net positive or a net negative?
I've been covering this industry as a journalist for a decade and a half and flying for over 40 years. All things considered, I've concluded that they're a net positive where they're used - primarily on short-haul flights of just a couple of hours - mostly because they get rid of that potential fight with the person in front and behind.
Long-haul flights, though, are different, and recline on these seats is absolutely here to stay, but with the added benefit of the extra shin clearance developed for the pre-reclined seats.
Just be a good airplane citizen and check behind you before reclining, recline slowly and smoothly, and put your seatback upright when everyone is having their meal, preferably without needing to be asked by the crew.
CNN
