What is a tailstrike and how do pilots stop them from happening?
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Last month, a State of Kuwait Boeing 737-900 was filmed performing its departure from Glasgow Prestwick airport after the COP26 summit. Unfortunately for the crew that day the take-off didn’t go quite according to plan and they managed to scrape the tail of the aircraft along the runway as they lifted off.
Tailstrikes are an ever-present threat to pilots of large aircraft on take-off, although statistically and arguably surprisingly, they are more common on landing. They can cause serious damage to aircraft and cost operators millions in repair costs and lost revenue from the aircraft being out of service.
Tailstrikes are more common in windy conditions, with longer aircraft being more susceptible. A serious tailstrike can cause damage to the rear pressure bulkhead – the diaphragm shape structure that separates the pressurised cabin from the unpressured tail section. The consequences of this could lead to structural failure of the aircraft fuselage.
However, raising awareness about the threat of tailstrikes and giving appropriate ground-based training to pilots in simulators can help lower the risk of the event happening for real on the aircraft.
The Art of Rotation
Aircraft don’t just get airborne by luck. We know exactly how much runway is needed, how much engine power to use and what speed to lift off at.
To calculate this, we use the Onboard Performance Tool (OPT). Before every take-off, the pilots must tell the aircraft how heavy it is and then calculate the speeds required to get safely airborne.
The OPT enables us to enter the airfield weather information and, using the take-off weight and trim setting given to us by the loading department, calculate the takeoff performance. This is one of the most critical stages of the flight. An error here could have serious consequences on the takeoff run.
By correctly calculating these figures we can know for certain that when we pull back on the control column, the speed known as Vr (rotate) will be optimal. Allowing our 220-ton aircraft to sink back just enough on its tail so that the nose can rise into the air and the aircraft will climb gracefully into the sky.
How exactly we do this comes with practice. First in the simulator and then in the aircraft.
When reaching the Vr speed, we pull back on the controls in a smooth and progressive manner. For most large jets, this is done at around 3° a second. This ensures that as the nose rises into the air and the tail sinks closer to the runway, enough lift is being generated by the wings to enable the aircraft to climb away from the ground before the tail hits the pavement.
The causes of tail strikes
To help operators reduce the risk of a tail strike event, a study was carried out into a number of tail strike events to try and determine if there were any common themes. Researchers considered environmental factors such as wind speed and direction, temperature and precipitation and also the weight of the aircraft, its trim (how the place is balanced) and speed.
They found that even though tail strikes can happen at all times of day and night, in good and bad weather, and to hugely experienced pilots, most happened to pilots who were relatively new to that particular type of aircraft.
Although a pilot may have several thousands of hours of flying experience, transitioning onto a new type of aircraft can be quite challenging. Sure –just like cars – the basic principles of flying an aircraft are the same. But driving a high-performance sports car requires quite a different set of skills to driving a truck. It’s the same with aircraft.
How an aircraft flies and feels, particularly in the critical stages when it is just a few feet above the ground varies significantly between types. Understandably, going from a Boeing 737 up to a 777-300 is quite a step up. As a result, pilots regularly spend several hours in the simulator honing their technique before they are let loose on the real thing.
However, it’s not just between the small and large aircraft where there is a marked difference in control. There can be a marked difference in variants of the same type, too.
Same type, different feel
For many years I flew the A320 family – the A319, A320 and A321. Whilst they are all legally the same type rating, they all fly quite differently from each other.
Being the base model, the A320 is probably the most ‘stable’ of the three. By that, I don’t mean that the other two are ‘unstable’, but merely that the A320 is the yardstick for how they fly. The A319 was similar to fly but when carrying a lighter load woud require careful thought on the approach, particularly when slowing down.
The A321, being the longest of the three did feel quite different to fly. As it was heavier, it handled turbulence better and some of my smoothest landings came on the A321. That said, to the inexperienced A321 pilot, it had a dark side. On landing, just after touchdown, it had a tendency to pitch the nose up. If you were not expecting this, it would be quite easy to scrape the tail. However, with more time spent on the aircraft, one learned how to deal with this.
This variation in handling can also explain why the previously mentioned study also found that the rates of tail strikes were higher for some types on take-off and for others on landing.
The study found that there were eight main causes for a tail strike: incorrectly set stabilizer trim on take-off; rotation at the wrong speed; excessive rotation rate; incorrect use of the flight director; unstable approaches; ‘holding off’ in the flare; mishandling of crosswinds and over-rotation during a go-around.
By focusing on these areas and giving crews proper training, pilots are able to reduce the risk of a tail strike occurring.
Tail Strikes on Take-off
Whilst most tail strikes happen on landing, there are still a number of factors that can cause them to occur on take-off. How the aircraft is set up for take-off, the speed at which the pilots pull back on the controls and pulling back on the controls too quickly can all lead to scraping the tail on the ground.
Incorrectly set stabilizer trim on take-off
To use a relatable example, aircraft are like a giant see-saw in a kids playground. If the weight at each end is the same, the see-saw stays horizontal over the central pivot. However, if the weight at one end of the see-saw exceeds the weight at the other end, the heavier end will drop to the floor.
If all the weight is at the rear of the aircraft, there’s a high chance that it could tip back onto its tail. If all the weight is at the front, the pilots will be unable to lift the nose at the critical stage of the take-off run. As a result, the passengers, baggage and freight must be loaded in a way that keeps the aircraft balanced.
However, this is still not quite enough. Aircraft are at their most fuel-efficient in the cruise with a slightly aft Centre of Gravity (CoG). With that in mind, they tend to be loaded in a way that will achieve this. The downside is that the aircraft might be slightly out of balance for take-off.
To fine-tune this, after calculating the take-off performance as detailed above, we set the ‘trim’ for take-off.
This means moving the entire horizontal stabilizer at the rear of the aircraft. This ensures that as the air starts to flow over the aircraft during the take-off run, the forces acting on it keep it in balance, resulting in a smooth take-off.
Rotation at the wrong speed
As mentioned above, rotating at the correct speed is vital in ensuring a safe take-off. However, if the pilots have calculated the Vr incorrectly, serious problems lie ahead. This error is most commonly caused by the incorrect input of the aircraft weight into the flight computers and the performance calculator.
If the weight entered is too low, the OPT will calculate that the aircraft can get airborne at a lower speed. However, when this speed is reached on the take-off run and the pilots pull back on the controls, the wings will not be generating enough lift for the weight that the aircraft actually is. The result: striking the tail on the runway.
Excessive rotation rate
As explained above, Vr is the speed at which the pilot flying gently pulls back on the controls to rotate the nose up into the air. This has to be done at exactly the correct rate. Rotate too slowly and we risk going off the end of the runway. Rotate too quickly and we risk striking the tail.
Tail Strikes on Landing
Tail strikes are more likely to occur on landing, partly due to the variability of the environmental conditions but also due to the pressures of the approach.
One of the main factors in incidents on landing is the aircraft approaching the runway too fast and too high, putting it in a ‘high energy’ state. This can easily lead to the aircraft going off the end of the runway, particularly if the surface is slippery after a heavy rain shower.
Landing at too high a speed also affects the way in which the aircraft handles, increasing the chance of a tail strike.
However, in most incidents like this, the situation develops because the pilots found themselves in an incredibly high workload situation and they run out of the capacity to make rational decisions and handle the aircraft correctly.
As a result, most airlines mandate that their pilots have the aircraft in a ‘stable’ state as they reach 1000ft above the ground. This means that it should be on the correct vertical profile for the approach, in the landing configuration (Gear down and landing flap set) and at the correct approach speed.
If these criteria have not been met, chances are it’s because the crew are maxed out and have lost situational awareness. Therefore they must abandon the approach, go-around and make a 2nd, safer approach.
‘Holding off’ in the flare
We all love a smooth landing. The passengers think we’ve done a great job and it works wonders for our egos. However, striving for that perfect landing can very quickly become a tail strike if a pilot isn’t careful. Just before we touch down, we pull back gently on the controls to raise the nose and slow the rate of descent.
Quite often we are carrying a little too much speed or there is a gust of wind. This can cause the aircraft to ‘float’ and keep flying along the runway just a few feet above the ground. The temptation here is to pull back on the controls, even more, to ease the wheels onto the paved surface, but by doing this the speed decreases and the tail gets closer to the ground, risking a tail strike.
When a pilot finds themselves in this situation the best thing to do is just allow the aircraft to settle onto the ground and accept it will be a little more firm than we’d like. Much better a firm, safe landing than one where we scrape the tail.
Mishandling of crosswinds
Crosswinds provide some of the most challenging conditions for pilots. Sudden gusts of winds can disrupt the flight path of the aircraft, requiring quick and assertive inputs from the crew. If handled incorrectly, it’s another thing that can put the aircraft at risk of a tail strike.
One of the best tactics in these conditions is the use of the rejected landing technique. This differs slightly from a go-around in that a rejected landing occurs very close to the ground or even after the aircraft has touched down whereas a go-around occurs higher above the surface.
By applying full power and holding the aircraft altitude level, the pilots can regain control of the situation before taking the aircraft back up into the air and making another approach. The video below demonstrates this perfectly:
Striking the tail of an aircraft can be costly for airlines, both in terms of repairs costs and loss of revenue whilst it is out of action.
As a result, understanding how to avoid these incidents is a key part of a pilots skillset. Training in the simulator helps us to practice scenarios in the safety of a ground-based environment to ensure that when we experience them for real, we react and respond in the correct way.
Featured Image – Getty Images
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