It is still unclear why the Cessna crashed into the Baltic Sea with four Germans on board. Flight safety expert Stefan Hinners considers pressure equalization problems to be likely. Observations by fighter jet pilots, however, point to a different tragedy.
FOCUS online: Mr Hinners, a Cessna 551 starts in Jerez de la Fronteira in Andalusia, destination Cologne, but flies over Cologne and crashes in the Baltic Sea off the coast of Latvia almost five hours after take-off. Previously, numerous attempts by military jets to contact the pilot had failed. What does this mean from an expert’s point of view?
Stefan Hinners: From what is known so far, the crash strongly indicates problems with the pressurization of the aircraft’s cabin. If there is a problem somewhere, depending on the flight altitude, the crew has very little time to prevent the crew and passengers from losing consciousness due to the drop in pressure.
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When is pressure equalization necessary?
Hinners: As a rule, the pressure equalization begins after take-off and keeps the pressure in the fuselage at a level that corresponds to that in the wild at a maximum altitude of 2500 – 3000 meters. It would not be mandatory up to 13,000 feet. However, the Cessna 551 is a jet with two jet engines.
These machines are very powerful and fly at similar altitudes and under the same rules as airliners. Depending on the load, an Airbus climbs at 2200 feet per minute, while the Cessna 551 climbs up to 3500 feet. You are very quickly at a height where pressure equalization is absolutely necessary.
Lawyer Stefan Hinners is a publicly appointed and sworn expert for flight operations, aircraft accident investigation and operational damage to aircraft. The Hamburg pilot himself flies as a private and commercial pilot and also holds the American and German pilot’s license for helicopters. He is also a recognized flight examiner from the German Federal Aviation Authority for single-engine and multi-engine aircraft under visual and instrument flight conditions.
What happens to the passengers if the pressure equalization doesn’t work?
Hinners: This is a devilish business. People lose consciousness very quickly without realizing the loss of control themselves. I’ve seen tests in the simulator where pressure equalization was restored just before the pilots lost consciousness.
They were already unable to operate the instruments, but thought they were always in control. If the pressure equalization does not work, the air pressure falls below the level that is essential for survival.
If the altitude is not reduced immediately, down to altitudes where the pressure is sufficient to provide people with sufficient oxygen, crew and passengers are doomed to asphyxiation.
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The Cessna, which was probably flown by the Cologne-based aviation entrepreneur Peter Griesemann, apparently had problems with pressure equalization about an hour after take-off near Toledo, as the Spanish newspaper “El Mundo” reports. What safety precautions are there for such a problem at altitudes above 13,000 feet?
Hinners: There is a clear signal in the cockpit. In the passenger cabin, the oxygen masks automatically fall out of the ceiling device when the pressure in the cabin rises above 13,000 feet, i.e. about four kilometers altitude.
However, this does not apply to the pilots. You have to put the mask on by hand. There is a so-called ‘quick donning mask’ behind each pilot’s seat, which can be pulled out with one hand in one to two seconds and placed securely over the mouth and nose. This short reaction time is essential for survival.
How much time do the pilots have to react?
Hinners: At a typical cruising altitude for jets, the time between the loss of pressure and the onset of loss of control for humans is only 30 to 60 seconds. Within this time, the moment of shock must be overcome and realized what actions are required next.
If, for example, the mask was not checked before the start or is in the holder, but the connecting tube is not locked or not locked properly so that no oxygen flows, then the time can become extremely short. At a typical cruising altitude, the oxygen supply is sufficient for around 20 minutes.
From the altitude of Bordeaux, fighter jet pilots not only report that they no longer had any contact with the pilots, but also that nobody was to be seen in the cockpit. Is it possible for an unconscious pilot to slump in his seat and become invisible from the outside?
Hinners: No, that’s actually impossible. The cockpit of the Cessna 551 is very small, you would always see the pilot and co-pilot, there is no space in the footwell or next to the pilot’s seats. At most, it is possible that the pilot, if he wasn’t wearing his seat belt, slumped to the side so that it seemed as if nobody was sitting in the seat.
That means the machine flew without a pilot – possibly from Bordeaux to the crash in the Baltic Sea off the Latvian coast, because the machine had probably run out of fuel. What could have happened?
Hinners: There are contradictory statements here, the pilot is said to have been seen over Denmark. If the information provided by the French fighter jet pilots is correct, this means that the pilot and co-pilot, if they existed at all, must have gone into the cabin.
There were only four people on board in the ten-seater: Griesemann’s wife, his daughter and one other person. Maybe he went to the back to help his daughter and the others because they were struggling. If so, this could have been a fatal mistake.
Hinners: It would mean that the pilot, who possibly steered the machine without a co-pilot, was not wearing a mask himself. In an attempt to help the family, Griesemann himself may have lost consciousness and could not have made it back to the cockpit.
The cockpit of this Cessna is extremely cramped. Even a sporty and flexible person needs a good ten seconds to get in and out safely without bumping into anything. Such an attempt to help could have had fatal consequences.
Is it even allowed to fly at the level of airliners without a co-pilot?
Hinners: Not in commercial air traffic. But this was obviously a private flight, so it’s up to the pilot to decide. As a rule, however, there is always a co-pilot on such flights. And for one reason: if there are problems, the workload for one pilot alone is extremely high.
Are there safety standards or training that are mandatory for pilots?
Hinners: There are two training courses per year that are mandatory for pilots of commercial flights. But not for private pilots. But even these are checked for their capabilities every two years for small aircraft, for flights in instrument flight and once a year for larger aircraft.
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According to information from FOCUS online, Griesemann, who was 72 years old, only recently returned to flying after a long illness. What does that mean for a pilot?
Hinners: There are certainly older pilots who are physically fit and resilient. An experienced older pilot may even be able to react much better than a young, inexperienced pilot. But in general, empirically, older people’s physical performance decreases. However, if someone has been ill for a long period of time, this may reduce their ability to perform.
However, it must be said that after an illness that significantly limits fitness to fly, an aeromedical expert must first reconfirm the medical fitness. This research is very comprehensive.
The crashed Cessna is 40 years old. Too old to be sure?
Hinners: Problems with pressure equalization are extremely rare in aviation. And if there are problems, they will by no means automatically cause the machine to crash. A drop in pressure is unpleasant, but can easily be managed by flying.
There is a so-called ‘Caution Warning’ – an alarm signal that automatically goes off in the event of a noticeable drop in pressure and cannot be overlooked by the pilots – in the event that they have not previously noticed the pressure drop on the pressure display or if it occurs suddenly. The Cessna Jets are extremely safe aircraft.
The aircraft are always subject to ongoing maintenance. In addition, general aviation aircraft only fly a fraction of the flight hours that a commercial aircraft flies per year and can therefore be operated for longer.
How did the accident dynamics develop in similar crashes?
Hinners: As I said, there are very few accidents that have to do with pressure equalization problems. I can think of three right now, including a 737 that crashed in Greece in 2005. And in all three examples, human error was a very important factor.
Failure in aircraft maintenance used to be a major factor in depressurization incidents, but this is almost no longer a contributory factor due to changing maintenance regulations.