Ask Captain Lim

Hi Capt Lim,

Regarding the Airbus A320 crash in BRAZIL this week, why did the pilot speed up to do a go around when he was already on the runway? He could have done all he could to slow the jet down.

Don A

Hi Don,

I don't know why the pilot decided to do what he did (going around when he was already on the runway) until the exact details are revealed by the black box. The communications and what transpired would be recorded by the CVR (cockpit voice recorder) and the technical details will be shown on the FDR (flight data recorder). Both the recorders are part of the black box.

I know many people will start to speculate on the causes of the crash (the runway was short and wet, one of the reversers was unserviceable, etc).

I overheard an aviation expert in CNN commented that the blame for the crash falls squarely on the shoulder of the runway condition. On the question of air safety, could one blame the environment for the misfortune?

Indeed the runway is short - only 6362 feet long (1939 meters). But that is within the stopping requirements of the Airbus A320 when the runway is reasonably dry.

When its landing weight is 66,000 kg, it requires only around 910 meters to land without wind corrections.

However, when the runway is wet, it would require 1240 meters. With 6.3 mm of standing water, the runway length must now be at least 1700 meters (5777 feet - compared to the runway length of 6362 feet) long.

So, if the pilot makes a misjudgment on the touch down - landing 250 meters further, there would be no more room for further error! He could not have done all he could to slow the jet plane down because he probably has reached his limits.

The landing distance calculations above do not take into account the use of the thrust reversers. So a failure of one reverser is insignificant unless the defective one leads to other unknown mechanical problems. If both the reversers were used, the landing distances would be further reduced by the following percentages: - dry runway - 3 %, wet runway - 8 % and very wet runway (1/4 inch) - 10 %.

Now, back to the issue of air safety. A professional Airbus A320 pilot must have all the above figures clearly in his mind when operating on such a restrictive environment. If he thinks the condition is unsuitable for the landing, he must not even attempt the approach in the first place.

There was also a report from the video showing that the plane was speeding very fast on the rain-slicked runway. Pilots are taught to go around by 500 feet above ground level if the approach was unstabilized (incorrect speed and wrong profile). If indeed he went around when he realized he was not stable (too high speed), he probably must have run out of runway to climb away safely.

Yes, I am only providing the supporting figures to speculate as to how critical it could be if a safety decision is made too late on a marginal runway. Well, only the black box will finally give the true picture of what went wrong.