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The B737 is probably my favorite aircraft and I'm always sure to never throttle past 100% of N1. I was told the aircraft is pretty much totaled if you take N1 past 100% but you can eke out that extra power for emergency purposes. Is that true? What are the consequences of exceeding 100% N1?
And what numbers should I be paying attention to for takeoff in a 737?
Your real question here should not be about a specific speed but about a specific thrust level. (see the comments)
Every engine will have 2 ratings a takeoff thrust rating and a maximum continuous thrust rating.
Takeoff thrust is self-explanatory. That's the level at which you can takeoff. The engine will only be rated for a few minutes continuously at takeoff thrust. After that time, you are supposed to reduce thrust.
Maximum continuous thrust (aka "max con" or MCT) is the thrust level at which the engine manufacturer will certify that you can operate for any length of time with no significant impact to the engine. Max con will be above cruise but below takeoff. For example, if one engine fails on a two engine plane, you'll need to run the other engine higher than a normal cruise thrust. Max con is the level that you will want to run at.
In other words, you can go to max con forever, but you can only go above max con (up to takeoff) for X minutes (where X is 5 or, depending on the engine)
So, what happens if you exceed max con thrust for more than X minutes? If you go a little bit past max con for a few seconds, probably nothing happens. If you go well past max con for several minutes, you can shorten the service life of the engine. i.e. you might have to take the engine off wing and overhaul it a bit sooner than you otherwise would have. The higher you go and the longer you sit there, the worse it will be. And if you go to full throttle for an extended period of time (hours), then you could total the engine.
One of the driving factors of the engine's life is the high pressure turbine. Problems there are low cycle fatigue, creep, and oxidation. All of these are made worse when the turbine gets hot. And the more thrust you are making, the hotter it will get. And the longer you sit at high power, the hotter it will get.
The consequences are always explained in the flight manual. It has graphs which specify what you should do if you exceed the speed, temperature, etc., by how much and for how long. For example (this is for FJ33-5A):
Note that the 100% mark is, in a sense, arbitrary. It does not necessarily mean the absolute max (even the 'normal' max), as can be seen from the example. (I don't know how it is for CFM56). This happens for several reasons; typically, the 100% value corresponds to a fixed RPM number for the whole family of engines. As the engine undergoes modifications, the permissible RPM may increase (or, in some cases, decrease), yet the 100% RPM number is usually not changed, moving the red line instead. In some cases, a civil engine is installed on a military aircraft, and is then allowed to run at, say, 108%, at the cost of much reduced lifespan and service intervals.
Sorry, could be wrong here, but given the thermo-resilience of the materials most engines are made from are essentially exceeded by overclocking for to long, the thermo-residue buildup eventually end up melting the engine; this is why there is redundancy built into the MCT for engine outage scenarios etc.
