Possible Clues:

• Bail out
• Retrieve army corps' signal
• Soldiers' signal recovery
• Secure (anag) — release
• Do you need a helping hand in the scree?
• Save for this, it's the engineer's sign to come in
• Take the engineer's tip and make a significant saving
• Free (from danger)
• Occasion for engineers to talk of salvation
• Green sack used regularly for delivery