In earlier days, a different type of wheel arrangement called conventional/taildragger landing gear were popular. It consisted of two main landing wheels in the front and one small wheel under the tail.

This type of wheel arrangement has some advantages such as the ability to land on rough runways, low cost of tail gear maintenance and you don’t need to worry about tail-strike. However there are some disadvantages, such as low forward visibility and susceptibility to serious ‘nose-over’ accidents if the pilot brakes aggressively during landing.

Every design change on an airplane or any other system is a tradeoff between some elements such as cost, technology, development difficulty, maintenance issues, safety, efficiency, etc. At present, tricycle undercarriage is the best suited design for a big commercial airliner.

Here is an illustration showing the body angle of both types of planes.

What causes a tail-strike? Boeing has done extensive research on this and the main reasons according to them are as follows. (You can read the detailed report here.)

During take-off

• Mistrimmed stabilizer. (Due to wrong weights, or an incorrect centre of gravity.)
• Rotation at improper speed. (Usually due to wrong calculation of weight or flap settings.)
• Excessive rotation rate. (Usually when an inexperienced pilot is transitioning from a different plane.)
• Improper use of the flight director.

During Landing

• Unstabilised approach. (Excessive airspeed, excessive altitude, sudden changes, etc.)
• Holding off in the flare. (Often happens when the pilot tries to achieve an extremely smooth landing.)
• Mishandling of crosswinds. (Landing in gusty winds.)
• Over-rotation during go-around. (Sudden change from landing to take-off can cause mishandling of thrust and angle.)

Tail-strikes during landing are more severe than the ones during take-off.

During Loading
Incorrect weight distribution during cargo loading can cause a tail-strike even before the plane starts.

Flight crews operating an airplane model that is new to them, especially when transitioning from unpowered flight controls to ones with hydraulic assistance, are most vulnerable to using excessive rotation rate and causing tail-strikes.

How are tail-strikes prevented?

All planes are equipped with a gyro horizon indicator which is often part of the Primary flight display. This gives the pilot crucial information about the angle, speed and altitude of the plane. If the plane takes off at the right speed at right angle, then it won’t cause tail-strike.

Some modern passenger planes have a tail-strike sensor which alerts the crew when the tail is too near the ground.

Some planes, which require a high angle of attack on take-off, are fitted with small tail wheels to prevent tail-strikes.

Image: Concorde with retractable small tail wheel.

Image: Boeing 737-900 with a tail-skid which acts like a bumper.

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Accidents

Image:- Damage to a B777’s fuselage due to a minor tailstrike

Tail-strike incidents usually do not cause significant damage and are not dangerous to passengers. But, it may cause financial losses due to the repair, maintenance and inspection costs. However, improper repair after a tail-strike causing structural failure have led to two major accidents.

Japan Airlines Flight 123 suffered explosive decompression 12 minutes into the flight and, 32 minutes later, crashed into a mountain near Tokyo. All 15 crew members and 505 of the 509 passengers on board died. It is the deadliest single-aircraft accident in history. Improper repair of the damages caused by a tail-strike which happened seven years earlier was the cause of this accident.

China Airlines Flight 611 disintegrated in mid-air and crashed into the Taiwan Strait 20 minutes after takeoff, killing all 225 people on board. This accident was caused by improper repairs to the damages caused by a tail-strike 22 years earlier.

Tenerife airport disaster was a fatal runway collision between two Boeing 747s which killed 583 people, making it the deadliest accident in aviation history. Although tail-strike was not the main cause of the accident; when the KLM 747’s pilots saw Pan AM 747 on the runway while they were trying to take-off, in desperation they prematurely rotated the aircraft and attempted to clear the Pan Am by climbing away, causing a severe tail-strike and ultimately the collision.

An example of major tail-strike incident

Image: Major tail-strike damages to a Singapore airlines B747.

This incident was the result of the first officer mistakenly entering an aircraft weight figure 100 tonnes lighter than that of the aircraft into his take-off speed calculations.

The captain then failed to pick up the error when he checked the calculation, the second officer did not check it and all three pilots failed to notice the difference between their own calculation and that of the flight management computer.

As a result, the captain “rotated” the plane to a takeoff angle at 123 knots (221km/h) rather than the correct 151 knots (272km/h).
With the plane failing to take off, it tilted 4 degrees more than normal, resulting in its tail striking the runway and dragging for 490m.
Source: Singapore Airlines tail-strike incident blamed on pilots – National – NZ Herald News

Planes are designed to withstand tail-strikes...

All major commercial airplanes undergo a series of tests to check if they can withstand a tail-strike.

Here is the 747-8’s tail-strike test video.