How do Airplanes keep fuel from freezing ?
Airplanes are exposed to very high temperature differences during a flight. When we think that the air temperature has reached extreme points, some questions come to mind. Does the fuel of the planes freeze? What happens if it freezes? As you can imagine, there are some solutions or precautions for this possible problem in the aircraft whose technology is constantly being developed and which is becoming more effective and safer day by day. Let’s go into a little more detail and examine it together.
Freezing Temperature of Fuel
Now that we know the temperature lapse rates in order to find what the air temperature is for various altitudes, what is the freezing temperature of aviation fuel? Well, it’s actually far below the freezing temperature of water.
According to AOPA, here is the average freezing temperature for popular jet fuels:
- Jet A (most commonly used in the United States): -40°C (-40°F)
- Jet A-1 (used worldwide): -47°C (-53°F)
- Jet B (most commonly used in Northern Canada for very cold temperatures): -60°C (-76°F)
- No. 3 Jet Fuel (most commonly used in China): -47°C (-53°F)
- TS-1 (most commonly used in Russia): -50°C (-58°F)
When the planes rise to normal cruising altitude, the outside air temperature can be -57 °C and even colder. This situation causes the fuel stored in the wings to cool down in time. If the freezing temperature drops 6 (six) degrees below, aircraft fuel will take the wax consistency and pumping fuel action to the engines of the aircraft will stop.
So there are some measures against this in planes. Briefly:
1. Extremely hot engine oil is circulated adjacent to fuel pipes through the system called “Fuel Oil Heat Exchanger” for cooling purposes. In this way, both the temperature of the engine oil is reduced and the fuel oil is heated.
2. The fuel in the fins is periodically pumped into the relatively hot central fuel tank located under the body of the aircraft.
3. The hot hydraulic pipes of the aircraft are designed to circulate around the fuel tanks.
Since the freezing of the fuel is extremely dangerous, the temperature of the fuel is constantly controlled with various sensors installed. And it can be checked from monitors. When a potential risky situation arises, pilots can increase the temperature of the fuel in the tanks by several maneuvers/procedures (by increasing the speed of the airplane or by reducing the flight altitude).
British Airways – Flight BA38
Thanks to the many measures taken, the number of accidents caused by the freezing of the fuel of passenger aircraft is almost nonexist with one exception.
A British Airways Boeing 777-200ER type aircraft, which was from Beijing Capital International Airport to London Heathrow Airport on January 17, 2008, had a sudden loss of power in its engines at the last moments of approaching the airport and had to make a very hard landing.
In the research, freezing in fuel pipes has been identified as the main cause of the accident.
The British Airways plane has passed through very cold air currents down to -74°C on the route between Beijing and London.
There always exists a small amount of water in the fuel tanks of the aircraft. This water has caused icing in the fuel pipes.
The interesting thing is that the Fuel Oil Heat Exchanger system mentioned above played a big role in the accident.
During the final approach, following the descent by applying relatively low power to the engines. The pilots gave the engines more power as in the normal procedure.
On top of that, the ice formed in the fuel pipes broke down and reached the entrance section of the Fuel Oil Heat Exchanger system and blocked it.
Due to congestion, both motors experienced power loss at the same time. The plane started gliding towards the runway after this incident that occurred 150 meters above the ground.
However, the plane failed to reach the runway and touched the ground a few hundred meters before the runway. 136 passengers and 16 crew members on board were successfully evacuated.
After determining the cause of the accident, the necessary improvements and updates were made in the Fuel Oil Heat Exchanger system. The entrance sections of the system were redesigned to cope with more ice.
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