Under what circumstances can the Initial Climb Area extend more than 2 nautical miles?

Question

While studying of FAA's Instrument Procedures Handbook, I noticed that on page 1-16 (Chapter 1: Departure Procedures) it defines the Initial Climb Area (ICA) as follows:

The ICA is the segment of the departure procedure that starts at the DER and proceeds along the runway centerline extended to allow the aircraft sufficient distance to reach an altitude of 400 feet above DER elevation and to allow the establishment of positive course guidance by all navigation systems. A typical straight departure ICA extends 2-5 NM from the DER along the runway centerline extended. It is 500 feet wide each side of the runway centerline at DER, then spreads out at 15°

However, I can not understand how it is possible for the ICA to extend more than 2 nautical miles, since the maximum horizontal distance covered by an aircraft until it reaches an altitude of 400 feet above DER elevation can be found by using the default minimum climb gradient of 200 feet/NM, which corresponds to 2 nautical miles. For an ICA to extend more than 2 nautical miles, a climb gradient of less than 200 feet/NM would be required, something that violates the rules imposed by FAA.

Could someone point me in the right direction?

Answer 1

The definitive reference for this stuff is the TERPS, and it says that the ICA can extend to 10NM(!). See 14-1-6(b):

Length. The ICA length is normally 2 NM, measured from the ICAB to the ICAE along RCL extended. It may be less than 2 NM in length for early turns by publishing a climb gradient. The ICA may be extended beyond 2 NM to maximum length of 10 NM. A specified altitude (typically 400 feet above DER) or the interception of PCG route must identify the ICAE.

I may have missed it, but I didn't see anything in the TERPS that explains how to set the length. However, the ICA definition from the IPH says (emphasis mine):

Initial Climb Area (ICA). An area beginning at the departure end of runway (DER) to provide unrestricted climb to at least 400 feet above DER elevation.

I couldn't find a formal definition of "unrestricted" but in ATC-speak it usually means "go for it" (e.g. ATC Orders 4-3-2(e)(1)). In this context, though, I think it means "no lower limit" rather than "no upper limit". In other words, the ICA will be extended to allow for 'worst case' scenarios where an aircraft's climb rate is extremely limited.

That suggests hot and high airports, and if you look at the ODPs for a famously high airport like Lake County (Leadville), CO (KLXV) at 9,934' MSL you'll see that the departure procedures are indeed almost straight, e.g. DAVVY ONE, which is more or less straight out for 20NM from runway 34.

Answer 2

I think I have reached to a conclusion concerning the explanation behind the rules which states that ICA can be extended up to 10NM (TERPS 14-1-6(b) and Instrument Procedures Handbook 1-16).

The first segment of a departure procedure is always a straight departure leg. In FAA 's PBN manual (Order 8260.58A) it states:

PBN Manual 5-2-1a. The ICA is aligned along the runway centerline for the distance required for a climb to 500 feet above airport elevation.

This implies that ICA might not necessarily end at the aforementioned distance, just that up to that distance it has to be aligned with runway's centerline.

In addition, PBN manual states:

PBN Manual 5-1-1c. The maximum allowable VA or VI leg length is 10NM.

And in TERPS:

TERPS 14-3-2 DR DEPARTURE splay outwards 15 degrees relative to the departure course from the end of the ICA. Limit the DR segment to a maximum distance of 10 NM from DER.

What I can decipher from the above, is that the first straight departure leg is considered an extension of ICA, and as such it should be less than 10 NM long.