Hi everyone, I've got a question that has been bugging me for a while. A typical UL limit load is +4 and -2 Gs. These loads are normally placarded and/or reported on the POH as loads that the pilot should care never to exceed, thus they do not represent (thankfully) the actual structural limits of the aircraft. And here comes my doubt: ultimate loads are usually reported as +6 -4 Gs: since our aircraft aren't made of glass or any other brittle material, I suppose all stressed components will undergo a certain amount of plastic deformation before literally splitting apart. So when they report 4Gs as operational load 6Gs as "ultimate" positive load, I can interpret it 2 ways, please tell me which one is correct: Scenario 1: Load test @4Gs: no yield, no failure. Load test @ 5.5: Gs: no yield, no failure Load test @ 6Gs: some yield seen (e.g. bent bolts, elongated holes) but the structure can still "stay together" perhaps another 0.5 Gs or more OR Scenario 2: Load test @4Gs: no yield, no failure Load test @5.5Gs: some yielded components are acceptable (e.g. bent bolts, elongated holes) but the structure must still "stay together" Load test @6Gs: the structure must stay together for three seconds before "folding up" I had always been convinced that Scenario 1 was the correct one until I read BCAR-S for which I copied and pasted the passage below: S 305 Strength and deformation a) The structure must be able to support limit loads without [detrimental] permanent deformation. At any load up to limit loads, the deformation may not interfere with safe operation. This applies in particular to the control system. b) The structure must be able to support ultimate loads without failure for at least three seconds. However, when proof of strength is shown by dynamic tests simulating actual load conditions, the three second limit does not apply. "The structure must be able to support limit loads without [detrimental] permanent deformation". I'd assume all permanent deformation is somehow detrimental! "At any load up to limit loads, the deformation may not interfere with safe operation". I hope they mean "elastic deformation" by this, because if it's plastic it would mean that I could see yield even below the 4G limit?? How "safe" would it be to fly around with bent bolts and elongated holes?