What Can Cause A Hard Landing?
We have all experienced a heavy bump on landing, often unexpectedly. Rather than being due to pilot error,…
We have all experienced a heavy bump on landing, often unexpectedly. Rather than being due to pilot error, or damaging to the aircraft, these are usually planned and made on purpose. This article takes a quick look at what causes hard landings and why we normally shouldn’t worry about them.
Hard landing due to descent rate
The simple reason for an aircraft making a ‘hard landing’ (often referred to by pilots as a ‘firm’ or ‘positive’ landing rather than ‘hard’) is the descent rate towards the runway. Normal descent rate at landing for most aircraft is around two to three feet per second, but aircraft can land safely at a faster rate than this, and often do.
The faster the rate at landing, the ‘harder’ the landing. Boeing, for example, quote a maximum descent rate of ten feet per second for the 737 and comment that flights crews often report a hard landing when exceeding four feet per second.
A hard landing can, of course, be due simply to pilot error, descending too quickly and/or not flaring sufficiently. Or there can be mechanical issues with the aircraft – such as happened recently with a Singapore Airlines A380 aircraft flying into Delhi.
This does happen, but often such a landing is intentional for one of several possible reasons:
Often better to land quickly – shorter runways and busy airports
During landing, descent rate is often slowed and the aircraft will ‘float’ or ‘flare’ at the final stage, as the nose is pulled up. If you watch smaller aircraft landing they will usually do this.
However, heavier aircraft often float less, if at all, and instead land at a higher rate of descent. There are several reasons for this. Firstly, ‘floating’ before touchdown will increase the use of the runway. It’s often safer to land quicker, leaving more runway for braking or any problems that arise during landing.
Secondly, getting the aircraft down quickly will minimize the utilization of the runway. It will land quicker, but also be able to exit the runway earlier. This is of high importance at busy airports with continuous landings.
Safer in wet conditions
Weather affects landing conditions. If the runway is wet, slippery or icy then it is normal to make a firmer landing. This will lessen the chance of skidding or hydroplaning and spin the tires quicker.
In foggy, or even dark, conditions this is an issue too. It can be harder to judge distances visually and again a firmer landing can be safer.
Wind or turbulence on landing
Wind direction and gusts can have a big effect on aircraft during the final stages of landing. In some cases, a harder than expected landing can be due to changing wind gusts during landing. It may be better to land quickly than risk an overrun.
Runway design may cause a hard landing
There are times as well when runway design can force a harder landing. A short runway makes a fast landing, with no / minimal floating important. London City airport, for example, has a runway only 1,300 meters long, so landing early and having the maximum distance to stop is important. Reagan National Airport (DCA) has a similarly short landing runway.
There are other runways too which slope upwards or downwards, such as at Naples, Italy. This can make any flaring during landing difficult, and aircraft will usually land hard.
Exceeding limits – it does happen
So, there are many reasons why a landing can be harder than passengers were perhaps expecting. The important thing to remember though is that this is usually nothing to worry about. Even landings which feel very rough are normally well within aircraft operating limits. And in most cases, the hard landing is intentional from the pilots, rather than any form of error or mistake.
If a landing is overly hard – and possibly reaches aircraft limits – it will necessitate a full inspection. This has happened recently with a new British Airways Airbus A350 aircraft flying into Tel Aviv. And also with a Lufthansa 747 flying from Frankfurt to Philadelphia.