Personally I just don’t understand why we aren’t seeing an increase in average jet aircraft speed, considering how efficient jet engines are now, and they continue to become more and more efficient. With this in mind, wouldn’t it make sense to increase the average speed of a jet (currently about 540 mph) to something closer to 700 mph (perhaps about 650 mph)? More efficient engines mean less fuel burn, so surely greater speeds are now achievable as they wouldn’t burn as much fuel?

An increase of even 100 mph would cut journey times, even if only by a small margin. Surely it’s worth it? We’ve seen turboprops increase in speed to over 400 mph, from roughly 300 mph, so why isn’t the same thing happening with jets? If we can’t achieve supersonic speed, we should at least attempt to reach near-supersonic.