Is the 737-900ER more aerodynamically efficient than the standard 900? The reason that I ask is that Vref of the 900 (with two thirds fuel and no passengers) is 142 knots, but the Vref of the 900ER in this configuration is only 137 knots, even though it is four tons heavier (with both auxiliary fuel tanks enabled).

On a side note, I really like how the engines sound a lot quieter in the 900 when compared to the 600, because they are further away from the cockpit. I cannot remember if I noticed that in the P3D version. The engines also sound different on take off, although that may be because the thrust at take off is significantly higher than the 600 (at the take off weights that I generally use; 90% compared to 84%). They also sound different when the thrust reversers are activated. I also like how I need to be careful to avoid tail strikes on take off. Once again, I do not remember noticing that in the P3D version.

Edited September 26, 2025Sep 26 by Christopher Low

The -900ER comes with the short field performance (SFP) package as standard. This comprises several modifications to the airplane that allow slower approach speeds and better stopping ability. This video has details:

https://youtu.be/rrEyYLpBIhk?si=FCVzdFftenBxNSkg

The main thing that drives the difference in ref speeds is the tail skid.  The tailskid in the straight -900 is fixed in one position, and the extra length of the aircraft creates a circumstance where an over rotation on landing can strike the aft fuselage instead of the tailskid.  This is a much larger problem from a maintenance standpoint.  So on the early -900s, Boeing artificially increased ref speeds to drive a flatter approach angle and mitigate the fuselage strike threat.  That, and the fact that it flies like a truck, are the main reasons most 73 pilots don't much like the straight -900s.

The -900ER (and -9Max) have a two-position tailskid.  It extends to the full extend position with the gear, and retracts after landing, and this is completely transparent to the pilots so you'll never know it's happening (and I have no idea if it's modeled in sim aircraft.). But this mitigates the fuselage strike threat and allows for appropriate ref speeds, which means the plane lands a lot nicer.

13 hours ago, martinboehme said:

The -900ER comes with the short field performance (SFP) package as standard. This comprises several modifications to the airplane that allow slower approach speeds and better stopping ability. This video has details:

https://youtu.be/rrEyYLpBIhk?si=FCVzdFftenBxNSkg

I had not considered that. I will have to check if this makes any significant difference with the standard 900, although I am generally more interested in flying the 900ER.

Edited September 27, 2025Sep 27 by Christopher Low