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I'm curious if there is ever a purpose to use full flaps like that? Was it a bit of an overkill?

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The MD-11 has one of the highest approach speeds, which is comparable to the 747-400 (Boeing), while having higher wing loading: 806 vs. 756 kg/m$^2$. In other words, the MD-11's wing is small, so flaps 50 is not an overkill.

The standard MD-11 landing flaps are either 35 or 50 depending on the weight, altitude, available stopping distance, etc.

Aircraft manufacturers don't usually go for overkill items. The bigger the flaps deflection the more loads and stresses there will be, and the stronger and heavier the flaps and wing support need to be made.

Further, the MD-11's flaps arrangement is covered in a NASA study, from which:

Because of high wing sweep, the slant angle on the inboard closure rib of the outboard flap is about 30°. When the flaps deploy, the slanted inboard rib exposes a forward-facing surface. The same out-of-streamline angle applies to the aft portion of the hinge fairings when the flap is deployed. (See fig. 1.24.) Both of these features degrade flap lift performance and cause drag. [emphasis added]

If McDonnell Douglas had went for an all-new wing for the MD-11, and not just adapt the DC-10's, it would have doubled the development cost, see: How much does it cost to design a jetliner's wing?

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Flaps 50 vs. Flaps 35 results in approximately a 5 knot reduction in approach speed in calm conditions.

I routinely use flaps 50, depending on weight, runway, and conditions.

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  • $\begingroup$ I'm curious, do you have training material or other resources describing procedures with those different settings? $\endgroup$
    – Manu H
    May 31, 2020 at 8:17
  • $\begingroup$ I'm not sure what the procedure is that you're looking for. The flap setting will depend on the weight, runway length and elevation, temperature, surface condition, etc. $\endgroup$
    – Will
    Jun 1, 2020 at 0:58
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    $\begingroup$ Volume IV of the MD11 FCOM (operating manual) is the performance volume, and contains 398 pages of charts and data. My material is all on an ipad and not in an exportable form. I use a program on the ipad for runawy data analysis for takeoff and landing information (TOLD data). We do have guidance on flap setting in most large aircraft, which is the minimum flap necessary setting for the conditions, and there's always other considerations such as windshear, go-around, etc, as well as increased noise during the approach with a high flap setting (more power required), higher fuel burn, etc. $\endgroup$
    – Will
    Jun 1, 2020 at 1:12
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    $\begingroup$ As noted above, the MD11 has the highest approach speeds of any commercial airliner. Greater flap settings mean the potential for more damage to the flap structure, as well. We do have an operational policy that if landing weights exceed 204,000 kg and the landing field is less than 8,500' long, we use flaps 50, and Medium or Max autobrakes (the exception being if weight is less than 181,000 kg, we only use minimum autobrakes to avoid damage to wheels and gear (specifically center landing gear drag link). $\endgroup$
    – Will
    Jun 1, 2020 at 1:13
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    $\begingroup$ @Will Integrate these comments into the answer, and you'll have something worth reading. Comments are ephemeral. $\endgroup$
    – T.J.L.
    Jun 1, 2020 at 13:36

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