Hung Start vs Normal Start - Do you know the difference ?

The video shows the difference between a Hung start and a normal start of a 737 engine.
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Left side - hung start
Right side - normal start

[@macieksoft]

Left one indeed hung start. N2 stays capped at 50% while EGT continues to rise. Also you can see that the start valve is kept open (because it cannot reach the starter cutoff).

[@shaofuchang515]

If for any reason the engine doesn't reach self sustaining speed the start is referred to as a 'hung' start and indicated by a low turbine RPM

[@franciscofurtado3232]

Shaofu Chang and really high EGT

[@clevelandaeromotive]

Cant anyone do a frick’n explanation video??

[@elyesdjazz]

on the left, the N2 didn't reach starter cutout speed. And N1 is low too.

[@fabrizio737]

showzasso man. tu e piloto?

[@james_orange]

Não, estava estudando manutenção de aeronaves na época que postei isso

[@sebastianbraggaar9726]

So what exactly is the difference?
What is happening in the hung start that shouldn't happen and why is it caused?

[@james_orange]

The N2 RPM is too low and EGT to high, if you consider the relation between both... Low RPM, that doesn't increase and the temperature increasing, you should abort the start... there is risk of compressor stall or even a surge... in the case of hung start not aborted, you must perform a large inspection in the hot section of the engine.. the combustion chamber may be damaged...

[@sebastianbraggaar9726]

thank you very much!
And what would be the difference between a hung start and a hot start?

[@richcam427]

Sebastian Braggaar if the EGT skyrockets as fuel is introduced, then it's a hot start. You would see the EGT gauge turn red and the N1 RPM window flash.

[@james_orange]

Exactly! It works basically like an explosion, in the hot start case!