Different carriers use different letters for the various fare levels they offer in each cabin, although the Y code is almost always still used for unrestricted economy travel.
The following are the different classes Elal uses for their economy cabin: (listed from lowest to highest which usually means cheapest/most restricted to more expensive/less restricted)
E (award ticket), W, U, O, G, N, H, L, V, K, B, Q, M, S, Y
business:
X (award ticket), R (upgrade), J, Z, D, I , C
first:
P (award ticket/ sometimes paid fare), A (upgrade/ sometimes paid fare), F