Originally Posted by rickair7777

Not for the CRJ. Somewhat complicated sensor logic prevents reverser deployment until some combination of wheel spin and WoW. It will let you at open them with the nose wheel off and I have actually deployed full reverse in that condition. My current company's SOP says to wait until the nose is down though, and I have no problem with that.

Remember...required runway length is always calculated without the TR's so you should never actually need them unless something else has gone significantly wrong. The conditions when you might be tempted to get early TR (contaminated RWY) are also conditions that could lead to loss of directional control.