NEW YORK ( TheStreet) --The Boeing (BA) - Get Boeing Company Report 767 is today considered an older aircraft that is rarely sold to passenger airlines, which invariably order its younger, sleeker, more fuel-efficient competitors.

Yet United Airlines (UAL) - Get United Airlines Holdings, Inc. Report passenger surveys continue to come across a surprising result: Among United's 164 widebody international aircraft and four widebody aircraft types, the 30 Boeing 767s that have gotten remodeled interiors since 2011 are the second most popular, after the 16 Boeing 787 Dreamliners, the newest and most innovative airplanes in the fleet.

After every flight, United sends an e-mail to nearly every passenger on the day following travel. The carrier doesn't specifically ask passengers whether they like the aircraft, but rather whether they enjoyed the various aspects of flight and how the experience might be improved.

The sample size is prodigious: An average of 8,000 passengers respond each day. The results showing happy 787 and 767 passengers are based on all of the surveys completed by passengers during 2015. For this story, only widebody aircraft survey results were considered.

Those results show aircraft interior configuration to be so important that it even leads passengers on remodeled 767s to extol every portion of the flight experience, including flight attendant service and the food. However, it remains true that the most important aspect of passenger flight evaluation is on-time performance. On a late flight, satisfaction invariably declines.

Mark Krolick, United managing director for marketing and product development, said the survey results reflect improvements the carrier has made as it has upgraded its 767 interiors.

"The 767 is a great airplane," Krolick said in an interview. "Every customer amenity is available on these airplanes. We have installed WiFi, seatback audio-visual on demand, power at the seats and larger overhead bins, and business class has lie-flat seats that are wider than they were previously.

"You put all those things together and you basically have a brand new aircraft," he said. "You go through the list of amenities we control and it is basically the same as the 787." However, 787s delivered by Boeing have larger windows, enhanced climate control and cabin air that is not heated by the aircraft's engines.

The coach class improvements are generally similar to those in business class, but the audio-visual screens are smaller, the lie-flat seats are lacking, and pitch is less --- 34 to 35 inches in economy plus, while economy is typically 31 inches with some occasional variations in both directions. Also, WiFi must be purchased in both business and coach classes.

Why would passengers enjoy a 767 experience more than the 777 experience? Krolick noted that the 767 has fewer middle seats because the seat configuration in coach is two-three-two. "It has more advantageous seating, due to the width of the fuselage," he said.

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Additionally, 777s typically fly longer missions, often several hours longer, which often leads to lower satisfaction, particularly among coach passengers.

As for United's 23 Boeing 747s, "they may be the most loved airplanes in the fleet, but in economy they do not have seatback entertainment systems," Krolick said.

However, the 747s have a personal device entertainment system, enabling passengers to connect their own cell phones or computers to the aircraft's onboard system, which is free and provides hundreds of hours of movie and TV programming.

United's 767 fleet includes three types:

Sixteen 767-400s were delivered to Continental between 2000 and 2002. They have two cabins and were reconfigured in 2011.

Fourteen 767-300s were delivered to United between 1998 and 2000. They have two cabins, and were reconfigured in 2012.

Twenty-one 767-300s, delivered to United between 1991 and 1993, are currently configured with three cabins for international flying, but will be converted to two-cabin. Each reconfiguration takes several weeks, during which the aircraft must remain out of service.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.