I’m not sure if this is still common practice or not, but why are/were plane instruments noted in their final positions when investigating an accident?
Would these dials not be tossed around like crazy during an accident? How do investigators know the dials are in their final positions from reading the information and didn’t just land in those positions during the accident? Do the instruments not move around more than I think?
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Not sure I know what you mean exactly – black boxes are digital recordings of everything that happened in the plane before and during the crash. It gives them the ability to make a fairly accurate model of the last few minutes / seconds leading up to the crash itself, so they can determine what went wrong. Add that to the cockpit voice recording (What the pilots are saying) and the accuracy improves. This is why the boxes are protected so well and are always what they’re searching for.
An instrument with a needle in a severe crash the needle would make contact with the gauge face leaving a mark indicating its last good position. This would let investigators know the status of systems on board.
It’s not the instruments themselves, but a log of all the instrumentation settings and changes for the entirety of the flight.
The flight recorder is a hardened box that contains a digital record of the electrical signals relating to the flight controls, the audio in the aircraft cabin and other sensors that the aircraft uses.
Modern commercial aircraft use electronic controls to operate the control surfaces of the aircraft. The signal sent and the position recorded of the surfaces are stored on the recorder.
The data can be used to determine what were the conditions of the instruments, the control surfaces and any cockpit conversations that occurred.
On aircraft that do not have FDRs, they are sometimes able to tell where the instruments were **at the point of impact** because the needles on the instrument will slap the back of the instrument and can often leave a mark.
Once FDRs became commonplace this procedure was no longer really needed.
The final position of the instruments can be a piece of the puzzle. The FDR and CVR might give enough clues, but the final seconds might be a gap in the timeline.
Some dials and instruments might be knocked around and be useless, but depending on the accident, the instruments might be mostly intact. In these cases, the instruments are locked in their last position, and the investigators might be cross-checked with other evidence to verify if they are accurate.
One example might be that a plane crashed because the flaps or slats were not correctly configured. The investigators don’t know this, but their analysis of the black boxes will reveal the speed and altitude of the plane, which will reveal a flight pattern that doesn’t match what should happen if things were correctly configured, so they would have to investigate reasons why the plane might not have enough lift. If the issue is with flaps, and they look at the controls and find the final position of the flaps and it matches what they theorise, it may explain the most likely cause.
In additional to being a investigation tool used in the past, many light planes still don’t have Flight Data Recorders and also in bigger planes the FDR can often fail to capture the last few minutes of data.
A broken instrument is like having a murder scene with a broken wristwatch. The watch may or may not have been set correctly before the murder, it may have been smashed before or after the murder but in the absence of other data it is a clue. Many investigations in the past have used final instrument readings and lever settings as part of their clues to reach a conclusion. Ultimately you want to have multiple clues that match up and corroborate each other.
However the latest jumbo jets have what’s called a Glass Cockpit – which mean that it’s all digital displays in the cockpit now. The position of physical levers like the flaps lever would still definitely be closely noted by crash investigators. If that had to become a critical part of the investigation then experts can take months analyzing the likelihood of whether that position is the final position as set by one of the pilots or whether there’s say stress damage to show that the lever maybe been moved by the impact.
I know some of the Electronic Flight Instruments could still be checked for final data via a chip on them but I don’t know if that’s standard on all of them or not, but that would involve sending it back to the original manufacturer to be checked in their labs.
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