I noticed this question here on aviation stackexchange, and I was wondering if there is a way to deduce the minimum IFR altitude (either 1000ft or 2000ft above obstacles, depending on whether or not the aircraft flies over mountainous areas) based solely on the information provided on a SID plate? Take, for example, La Guardia Five Departure (here is its textual description and here its take-off minimums).

Could someone point me in the right direction?


I understand that it is not required for a pilot to be aware of the minimum IFR altitude if he is following a SID. Perhaps I am overthinking it, but I am asking because I would like to know if, theoretically, an aircraft would have the right to climb with a climb gradient less than the standard (200 FPNM) while following a SID, if

A: There is not any other minimum climb gradient assigned

B: He is above 1000ft or 2000 ft (the aforementioned "minimum IFR altitude")

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    $\begingroup$ I'm not sure if I understand the question: if you're following an instrument procedure - or an airway - then you fly whatever altitude it requires. Or whatever ATC tells you to fly, of course. The 1000/2000 thing is a 'default' if you aren't following an explicit procedure or instruction (see 91.177). So I don't really know what the "minimum IFR altitude" would even mean to an aircraft following a SID. If you can clarify that, someone may be able to help. $\endgroup$
    – Pondlife
    Aug 10 '18 at 15:10
  • $\begingroup$ @Pondlife thank you for your comment. I will edit my question in order to make it clearer. $\endgroup$ Aug 10 '18 at 17:49

It's really an apples to oranges question. A SID always has an initial segment below the minimum IFR altitude, because it is a departure route. STARs are similar in that regard. There is no implied minimum IFR altitude on either SIDs or STARs (Not to be confused with MEAs). This also applies to approach plates, which have a minimum safe altitude, which you hopefully never have to use.

The correct method to determine the minimum IFR altitude for a course to be flown would be to plot a point-to-point route, and provide 1000/2000 foot above any obstacle within four nautical miles of the centerline of the route. Keep in mind that the "mountainous areas" depicted in the AIM are a quick reference for pilots, and differ substantially from the actual areas described in FAR 91.177.

The best pilot-available old school method would be to break out the sectional chart, because it has obstacle heights on it, and a navigational plotter. I've done that as a controller on several occasions.

Modern GPS has the capability to show your altitude above terrain, and can be used to obtain the same basic results. As an example, I once had an aircraft fly a point-to-point route under VFR-on-top, and he stayed below my radar coverage for about 90 miles. When I'd ask him for position and altitude information, his reports were consistent with 1000 feet above terrain, every time (there is no "wrong altitude for direction of flight" below 3000 AGL (FAA 7110.65, 4-5-2)). Kinda cool.


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