Investigators said the captain, Abid Sultan, wept during the flight after his skills had been questioned by a co-worker.
This mistrust and stress led him to continuously smoke in the cockpit and also suffer an emotional breakdown several times during the flight, their report said.
The 12 March flight from the Bangladeshi capital of Dhaka crash landed at Kathmandu airport and skidded into a football field where it burst into flames, killing 51 people in the deadliest aviation accident in the Himalayan nation for decades.
The captains constant monologue led to the total disorientation of the co-pilot, who was flying the plane when it crashed. Prithula Rashid had only recently qualified and had never previously landed at Kathmandu airport.
The draft copy of the final investigation report concluded the US-Bangla Airlines captain was under stress and emotionally disturbed after a co-worker had questioned his reputation as a good instructor.
During the short flight, Sultan a former Bangladesh air force pilot who was also an instructor for the airline talked non-stop as he tried to impress upon the junior co-pilot his competence and proficiency.
Nepals only international airport lies in a narrow bowl-shaped valley with the Himalayas to the north, making it a notoriously challenging place to land.
As the Bombardier Dash 8 Q400 turboprop approached the runway it made a last-minute change of direction, failed to sufficiently reduce its speed and necessary landing checks were not carried out, investigators said.
The report revised the final death toll up to 51, including both pilots. Twenty passengers miraculously escaped the burning wreckage but sustained serious injuries.
Conflicting reports emerged shortly after the crash suggesting confusion between the pilot and air traffic control might have caused the disaster.
The report said air traffic control did confuse the two ends of the runway referred to as Runway 02 and Runway 20 but concluded this had no impact on the flight.
A source at Nepals tourism ministry, which led the investigation into the crash, confirmed the authenticity of the draft.
The accident was Nepals deadliest since September 1992, when all 167 people aboard a Pakistan International Airlines plane were killed when it crashed as it approached Kathmandu airport.
Just two months earlier a Thai Airways aircraft had crashed near the same airport, killing 113 people.
Nepals poor air safety record is largely blamed on inadequate maintenance and sub-standard management.
Accidents are common and Nepal-based airlines are banned from flying in European Union airspace.
Rescuers pulled bodies from the charred wreckage of the plane, operated by Bangladeshi airline US-Bangla, after a raging fire was put out.
The airline has blamed air traffic control, but the airport says the plane approached from the wrong direction.
Flight BS211 veered off the runway while landing on Monday afternoon.
The exact cause of the crash remains unclear and Nepalese Prime Minister KP Sharma Oli promised an immediate investigation.
However, a recording of the conversation between the pilot and air traffic control minutes before the plane crashed suggests some misunderstanding over which end of the sole runway the plane was cleared to land on.
Moments before the plane crash-landed, an air traffic controller is heard in the recording from air traffic monitor LiveATC telling the pilot: "I say again, turn!"
Twenty-two people were treated in hospital for injuries, police spokesperson Manoj Neupane said.
The plane, which was flying from the Bangladeshi capital, Dhaka, was a Bombardier Dash 8 Q400 turboprop and was 17 years old.
The plane landed at 14:20 local time (08:35 GMT).
The aircraft was permitted to land from the southern side of the runway flying over Koteshwor, but it landed from the northern side, Sanjiv Gautam, director general of the Civil Aviation Authority of Nepal said.
However, US-Bangla Airlines chief executive Imran Asif blamed Kathmandu air traffic control.
There were wrong directions from the tower. Our pilot was not at fault, he told reporters at his office in Dhaka.
Our pilot is an instructor of this Bombardier aircraft. His flight hours are over 5,000. There was a fumble from the control tower.
Airport general manager Raj Kumar Chettri said that the plane hit the airport fence before touching ground.
The plane should have come from the right direction, he said.
One of the survivors, Nepalese travel agent Basanta Bohora, described from his hospital bed what he had experienced.
After a normal take-off from Dhaka, the plane had begun to behave strangely as it approached Kathmandu, he said.
All of a sudden the plane shook violently and there was a loud bang afterwards.
I was seated near the window and was able to break out of the window, he added.
I have no recollection after I got out of the plane, someone took me to Sinamangal hospital, and from there my friends brought me to Norvic hospital. I have injuries to my head and legs, but I am fortunate that I survived.
The plane was carrying 67 passengers and four crew.
It is now known that 33 of the passengers were Nepalis, 32 were Bangladeshi, one was Chinese and one was from the Maldives.
Among the 22 people injured, some are in a critical condition.
An airline worker said he saw two or three people fall or jump from the windows of the burning plane.
Its airline companies are banned from flying within the European Union.
There have been many aviation incidents in Nepal, but this is the deadliest since a Pakistan International Airlines plane crashed on approach in September 1992, killing all 167 on board.
Earlier that same year, a Thai Airways plane crashed near the airport, leaving 113 people dead.
Pilots say that landing at Kathmandu airport can be challenging because of the mountainous landscape.
Aviation incidents in Nepal include:
February 2016: Twenty-three people were killed when a small passenger plane crashed in mountainous western Nepal
March 2015: Lucky escape for passengers after plane skids off runway in fog in Kathmandu
February 2014: Bodies of all 18 people recovered after small plane crashes in western Nepal
September 2012: Plane heading for Everest region crashes on the outskirts of Kathmandu, killing all 19 on board
May 2012: Fifteen people die when a plane carrying Indian pilgrims crashes in northern Nepal
September 2010: Sightseeing flight crashes into a hillside near Kathmandu
September 2006: All 24 people on board a WWF helicopter die when it crashes in eastern Nepal
What is US-Bangla airlines?
The carrier launched in July 2014 and its slogan is "Fly Fast, Fly Safe".
Its first international flight was in May 2016 - to Kathmandu.
It now flies to airports in South and South East Asia and the Middle East.
Tourism Observer
