enter image description hereOn the PLMTO3 SID out of KCHS, Rwy 15 has standard takeoff mins.

From the AIM 5-2-9.e.1.

Unless specified otherwise, required obstacle clearance for all departures, including diverse, is based on the pilot crossing the departure end of the runway at least 35 feet above the departure end of runway elevation, climbing to 400 feet above the departure end of runway elevation before making the initial turn, and maintaining a minimum climb gradient of 200 feet per nautical mile (FPNM), unless required to level off by a crossing restriction, until the minimum IFR altitude.

My question is, do I need to ensure my aircraft can maintain 200FPNM up to the MSA, which would be 3100MSL, or just to the MOCA from PLMTO to Grand Stand VORTAC.

My thought would be that I have to ensure that the aircraft can make 200FPNM to the MSA since there are no MOCAs or MEAs published from JAYLN to PLMTO. But If that is the case then why do they even bother publishing a MOCA from PLMTO to CRE. There would be no point to climb 200FPNM to the MSA and then descend after crossing PLMTO.!]2


2 Answers 2


The Pilot/Controller Glossary defines:

MINIMUM IFR ALTITUDES (MIA)- Minimum altitudes for IFR operations as prescribed in 14 CFR Part 91. These altitudes are published on aeronautical charts and prescribed in 14 CFR Part 95 for airways and routes, and in 14 CFR Part 97 for standard instrument approach procedures. If no applicable minimum altitude is prescribed in 14 CFR Part 95 or 14 CFR Part 97, the following minimum IFR altitude applies:

  • a. In designated mountainous areas, 2,000 feet above the highest obstacle within a horizontal distance of 4 nautical miles from the course to be flown; or
  • b. Other than mountainous areas, 1,000 feet above the highest obstacle within a horizontal distance of 4 nautical miles from the course to be flown; or
  • c. As otherwise authorized by the Administrator or assigned by ATC.

The only part of the route which has an altitude "published on aeronautical charts" for the "airway and route" of the PLMTO3 departure is the segment from PLMTO to CRE (which technically isn't even part of the overall SID, it's a transition route). That means for the rest of the SID up until PLMTO the MIA is going to be either bullet point b or c from the definition, which in either case is going to end up being 3000' MSL as you pass northwest of a pair of antennas in the vicinity of LOIRN. (If not for those antennas the MVA would be down at 1600'.)

Note that you have a good 12 or so track miles to climb from CHS, at essentially sea level, to a point midway between JAYLN and LOIRN, at 3000'. Depending on how long you wait to start the lefthand turn once you depart Runway 15, that's 250 FPNM or even less. You can do some more precise plotting using the VFR sectional and Skyvector if you really need to, or you can just plan for 250 FPNM and call it a day.

  • $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Aviation Meta, or in Aviation Chat. Comments continuing discussion may be removed. $\endgroup$
    – Jamiec
    Commented May 24 at 8:56

In all cases continued obstacle clearance is based on having climbed a minimum of 200 feet per nautical mile to the specified point and then continuing to climb at least 200 foot per nautical mile during the departure until reaching the minimum en route altitude unless specified otherwise.

The departure route has all aircraft climb to and maintain 4000. So you need to keep up the gradient until reaching 4000. The MSA does not appear anywhere on this departure and it's not a great idea to start looking at approach charts and trying to extrapolate from them to cheat on your minimum climb gradient.

MOCA's aren't left off of charts just because they might not be useful in some specific situation. If you start picking up icing right after PLMTO knowing the MOCA would be very useful indeed!

If you're part 91 and not assigned a SID, you legally don't need to respect takeoff minimums and can DIY your own approach (let's not discuss the wisdom of this for now). This may well involve looking at approach charts or VFR charts to figure out the minimum safe altitude beyond which you won't hit anything. But this isn't flying the SID- if you are assigned the SID and accept it without telling ATC you can't maintain the required climb rate, you accept the required climb rates until you are en route. This means up to 4000, and then up to 5000 once past PLMTO unless you are cleared to a lower altitude.

  • 1
    $\begingroup$ Disagree that the gradient applies up to the top altitude of the SID. That altitude is for ATC procedures, i.e. traffic separation, rather than obstacle avoidance. The minimum IFR altitude is based on obstacles rather than traffic. $\endgroup$
    – randomhead
    Commented May 18 at 3:45
  • $\begingroup$ @randomhead The minimum en route altitude is also based on such things as radio communications and navigational signal availability. If not the top altitude of the departure, what other altitude could it be? It's clearly not the MOCA after PLMTO since that doesn't even provide obstacle clearance until after PLMTO. And it doesn't make sense for it to be the MEA after PLMTO since anyone doing this departure will level off below that. $\endgroup$
    – Chris
    Commented May 18 at 4:54
  • $\begingroup$ Where are you getting that phrase "minimum en route altitude" which you quoted in your answer? Both the AIM and the IPH use "minimum IFR altitude." Edit: I see you're getting it from AIM 5–2–9f rather than 5–2–9e1 referenced by OP. I'd contend that the language which matches across the AIM and the IPH is the better one to look at. $\endgroup$
    – randomhead
    Commented May 20 at 14:10

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .