Although these red triangles lined up along the fuselage are among the curious subjects about airplanes, it is not known what they are really used for.
There is a lot of misinformation about these triangles. Despite urban legends such as “The joining points of the fuselage of the aircraft”, “If the plane lands on the water, it will sink up to the sticker levels”, the situation is slightly different from those mentioned.
During the operation, some unwanted and abnormal events such as hard landing, leaving the runway and crushing can be experienced in airplanes as a result of technical malfunctions, pilotage errors, bad weather conditions.
Depending on the situation of the accident that occurred, more than the amount of load that the aircraft can resist may affect the structural elements of the aircraft and this may disrupt the symmetry of the perfectly designed aircraft.
A twisted wing of an asymmetrical airplane cannot react correctly to aerodynamic loads, a displaced center of gravity disrupts the stability, a deformed fuselage may be exposed to further stress.
Since all these situations are scenarios far from a healthy operation, it is vital to perform symmetry checks after the mentioned accidents.
These red triangles, called as leveling triangles are some of the points determined for symmetry control. There are similar points on the tail area, landing gear, pylons, engine cowlings and wings.
Targets are installed on these points. One of the measurement devices (telemeter, distance meter, theodolite, etc.) is placed at the points determined by the manufacturer in the left front, left rear, right front, right rear areas of the aircraft and the distance to the targets is measured and recorded.
The recorded data is sent to the manufacturer. If the dimensions show asymmetry, instructions for proper repair are taken from manufacturer or if it cannot be repaired, the aircraft says goodbye to service life.