Part of the Pitch Trim Runaway checklist for the E-Jet family states that Category II ILS approaches are prohibited if neither pitch trim channel is available:

If both pitch trim channels are failed:

Cat II Approaches are prohibited.

[E170/175 QRH, page 8-32, quoted in page 2 of NTSB ASR-20-01]

Why are ILS-II approaches (but not ILS-I or ILS-III approaches, or any non-ILS approaches) prohibited in an E-Jet with inoperative pitch trim, even if adequate elevator control is available to do so safely?

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    $\begingroup$ Are you sure that Cat III approaches are allowed in that condition? Typically, Cat III requires basically everything to be operative, unless there is some pretty unusual redundancy in the aircraft. Wouldn't be surprised if one channel out removes Cat III, and then losing the 2nd channel takes out Cat II. Just a guess, but the list of things required for Cat II that aren't needed for Cat III, while not empty, isn't very long in most cases. $\endgroup$ – Ralph J Feb 4 at 3:39
  • $\begingroup$ @RalphJ: In that case, one would expect to see "Cat III approaches are prohibited" or something similar at an earlier point in the Pitch Trim Runaway checklist, which isn't the case. $\endgroup$ – Sean Feb 4 at 3:43
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    $\begingroup$ If it's not certified for CatIII it won't make any mention in the first place. If the airplane didn't have head-up guidance, it can't be cert for CatIII. $\endgroup$ – John K Feb 4 at 3:55
  • $\begingroup$ @JohnK: HUD or (more commonly) triple-string autoland. $\endgroup$ – Sean Feb 4 at 3:56
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    $\begingroup$ I see cockpit photos of E-175's that have HUD's in them, but the photos I see of Republic E-175 cockpits don't show a HUD. Unless you know that the Republic aircraft in the report was both equipped and approved for Cat III ops, then the inference behind the question seems a little baseless. If the crew can't fly any form of Cat III approach anyway, you wouldn't expect the checklist to address it. $\endgroup$ – Ralph J Feb 4 at 4:06

Looking at the report, the airplane does not appear to be certified for CatIII in the first place (it would have to have Head Up Guidance and not that many do - the CRJs are the same) so the QRH doesn't need to mention an approach category that the airplane can't do anyway.

As far as CatII goes, the approach with no pitch trim is going to have to be flown by hand, and probably with the existing trim speed different from Vref, unless the trim failure happened while on final while already trimmed to Vref. So depending on how far away your current, fixed-due-to-failure trim speed is from Vref, you are going to have the hand fly an ILS while holding 5, 10, 15, 20, 30 pounds of force on the column to maintain glide slope at Vref.

This is quite a challenge because the slightest relaxing of concentration will cause you to relax your push/pull a bit and make you drift high or low. It's enough of an ordeal to do this and stay on glide slope right down to 200 ft. To hold it down to 100ft, the normal CatII decision height, is pushing it, so the approach is prohibited.

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  • $\begingroup$ So the problem isn't with it being an ILS approach, but, rather, with it being an approach to very low minima in an out-of-trim aircraft? $\endgroup$ – Sean Feb 5 at 2:41
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    $\begingroup$ Pretty much. Keep in mind that Cat II approaches generally require all of certain key systems working so there will be various types of system failures where you have to stick to Cat I minima. If you peruse that QRH more you should find a number of conditions where that prohibition statement for Cat II appears. $\endgroup$ – John K Feb 6 at 4:51

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