Over the years I have picked up my car(s) after service or repairs only to find several days later a tool left in the engine bay , it wasn't often ,
probably only half a dozen times .
You would go into the hangars and they had mobile tool cabinets , each tool had a tool outline painted , when the aircraft was zipped up
a check was made to ensure all tools were accounted for before the aircraft could be signed off .
Years ago the Australian authorities issued pilots with what we called the "Crash Comic" , an aviation safety digest , I remember a accident report
on a fatal Chipmunk aerobatic event , the pilot had a good record and was proficient at aerobatics , tests revealed that no medical event was involved .
Examination of the wreckage discovered a 20 cent coin in aft fuse , control was by bellcrank and tubular push rods , as the rod moved through it's normal travel
it moved up and down , an elongated hole was in a bulkhead to accomodate that travel , indent markings were found on the coin , the rod , and the bottom
of the hole , the summary was that a mechanic working in the fuse had a coin in his pocket that fell out , and purely by chance during aerobatics lodged in the
elongated bulkhead hole and limited the rod's movement , thus pilot had no control and it went in .
In 1969 the Saturn 5 had an instrument/control ring it included a computer that had the memory capacity of a tiny shopping calculator , it powered men to the moon .
In one early firing an igniter line came adrift from one of the 5 second stage engines , that engine began to faulter , that was detected and the computer sent a
message to shut down the engine , unfortunately all 5 engines were serviced by identical cables of the same length , during assembly there was a mix up ,
the message went to a good engine , so the second stage ended up with 2 dead engines .
The rocket started to pitch down , but that small computer regained control , rectified the pitch and it went into orbit .
The Space Shuttle used a old Computer chip ( possibly the 3086 , but I'm not sure ) it took several years to write and purify the software to a man safe
standard , as the years progressed chip stocks were depleted and manufacture lines had closed years earlier , NASA ended up having to search
for stocks of chips and it was reported they had to resort to secondhand chips .
The Australian version of the F-111 ended up with about 1.1 million lines of software code , thats a lot , however , last I heard
the F-35 had 24 million lines of code and that was before the gun was integrated into it .
You can imagine the effort that goes into debugging and purifying all that code , to remove errors , bugs , and conflicts , and that task has to be done
thoroughly as the end product will be flying frequently over populated areas with live munitions , or worse .
A modern Miljet might be designed and built in as little as 4 or 5 years , but the integrated systems , avionics , fly by wire , computers , and software
can take over 15 years to sort out . Some will remember the saga with those systems in the B-1 bomber , it dragged on for many years .
The "E" jet is a nightmarishingly complex beast .
Cheers
Karol