Hard Landing unstable approach

The most spectacular A380 Hard Landing with an unstable approach 

A hard landing occurs when an aircraft hits the ground with a greater vertical speed and force than in a normal landing.

So, a Hard Landing, in some regions referred to as a heavy landing, is a landing in which the manufacturer's touchdown limitation, expressed either as a rate of descent or as a 'g' loading value, has been exceeded. A hard landing has the potential to result in Loss of Control and/or aircraft damage, and will necessitate a manufacturer defined hard landing inspection.

Criteria of a Hard Landing

Almost all of us, either as pilots or as passengers, have experienced what we may have considered a less-than-ideal landing. These might have been manifested in a firm or bounced touchdown, a sudden longitudinal swing to realign the aircraft with the runway centreline, overly harsh deceleration, or even the unexpected displacement of loose articles or the deployment of some of the passenger oxygen masks. Whilst uncomfortable for most, and potentially frightening for some, these events seldom cross the threshold required to be classified as a hard landing. In some situations, such as during a landing on a contaminated runway, the firm touchdown may have been intentional.

As stated in the definition above, a hard landing is classified as the exceedance of a manufacturer limitation, which will vary by the category and purpose of the aircraft. For example, the hard landing threshold for an aircraft such as the MCDONNELL DOUGLAS F-4 Phantom, designed to land on an aircraft carrier, could be expected to be higher than that of a commercial airliner such as the MCDONNELL DOUGLAS MD-11. That said, based on certification criteria, the hard landing threshold is the same for virtually all commercial pattern aircraft and is expressed either as a touchdown 'g' loading of 2.6, or as a touchdown rate of descent exceeding 600 feet per minute (fpm), for landing weights up to the certified maximum for the aircraft type. For aircraft that are certified to conduct precautionary or emergency landings at weights above their normal landing limitation, the hard landing threshold is reduced to 1.7g or 360 fpm in the overweight condition. Whilst an exceedance of these values will trigger a mandatory hard landing inspection, many manufacturers also publish one or more cautionary thresholds at trigger values progressively less than the hard landing limit. Breaching a cautionary value will result in a supplementary inspection that is commensurate in scope with the severity of the event.

Cause of a Hard Landing

The most common cause of a hard landing is an unstable approach. Amongst other reasons, these can occur due to tailwind, a "rushed" approach, an attempt to comply with an overly demanding air traffic control clearance, adverse weather conditions or the improper use of automation. Abnormal speed or excessive rates of descent can make execution of the landing flare more difficult as the usual visual cues may be skewed or accelerated and the aircraft response to control inputs somewhat different to that normally experienced; that is, the input may cause the aircraft to balloon or, conversely, fail to arrest the descent. Gusty winds, active precipitation and reduced visibility can all make execution of the landing more difficult and can, therefore, increase the potential for a hard landing.

Prevention of a Hard Landing

There are a number of ways to help reduce the likelihood of a hard landing. Some of these are as follows:

Ensure that a stabilised approach is flown. If the criteria for a stablised approach, as mandated in the company Operations Manual, have not been achieved by the prescribed height above runway, the approach should be abandoned and a go around initiated.
Use manufacturer recommended landing configuration, approach speed, and speed additives appropriate to the runway available, aircraft weight, and any residual airframe icing.
Use manufacturer recommended speed additives appropriate to the reported wind speed and gust increment.
Execute the flare at the manufacturer recommended wheel height. Avoid an excessively high (or low) flare height.
Avoid an extended hold off.
In the event of a bounced landing, follow manufacturer recommendations for recovery. Baulked landing protocols may be necessary to prevent a hard landing.