Everyone knows that the purpose of these triangles is to show to the cabin crew the aircraft locations where they should look out through the windows in order to check the status of the wings, namely, the leading and trailing edges condition (i.e. position, ice contamination, etc).
But #DYK from a regulation point of view, there is no requirement to keep the triangles in the cabin except if they are required by a crew procedure (which is the case only for A300/A310 aircraft in Airbus family).
The reason for the presence of these markings in A320 aircraft is historical. On A300/A300-600 and A310 aircraft, the slat/flap position indicator (SFPI) is a mechanical unit, which can lack precision. External markings are necessary in case of loss of slat (or flap) surface position indication. The triangle marking on the cabin lining was necessary to indicate to the crew the proper position to observe the external markings in order to avoid misinterpretation due to parallax errors.
For A320 Family aircraft, the slat/flap position indication is accomplished through high reliability equipment (IPPU - Indication and Position Pick-up Unit - and ECAM upper display) and therefore external markings and triangle in the cabin are no longer required.
Nevertheless, A320 family airplanes are still delivered with these triangles, rather by aeronautical tradition than by necessity.
System Support Analyst
2moPoor people. Seems like the plain crashed on someone’s private house. I didn’t see any general emergency for this flight. Wonder what had happened to the aircraft. Awaiting for investigation report