Wait — option a says DOI = 114.8 → difference = 2.4. That means Crew index = 2.4. Then 2.4 = (410 × 142) / CF → CF = (410 × 142) / 2.4 ≈ 24,258. So CF = 24,258. Then BEM index = (34,560 × arm_BEM) / 24,258 = 112.4 → arm_BEM = (112.4 × 24,258) / 34,560 ≈ 78.9 m — plausible.
Therefore, this question uses a . But in the real EASA bank, they predefine that the Dry Operating Index is directly given by loading table or simple addition of mass and index using: easa atpl question bank
Index formula typically: , but in this question bank, they provide index directly for BEM and arm values for others. We must compute additional moment index from crew: Wait — option a says DOI = 114
Total DOI = BEM index + Crew Index = 112.4 + 5.8 = ? That doesn’t match any option — contradiction. So CF = 24,258