Definition
An optical illusion seen in an automatic direction finder (ADF) when the aircraft passes directly over the station being received. As the aircraft crosses overhead, the ADF needle becomes erratic and swings rapidly, then settles pointing aft once the aircraft has passed the station. The momentary fanning or sweeping of the needle is called the blossom effect.
Plain English
When you fly directly over a radio station, the ADF needle briefly goes wild before settling down to point behind you. That short period of wild swinging is called the blossom effect.
Context Anchor
Seen in radar and airborne weather radar discussions, especially when interpreting the size and shape of strong returns.
Derivation
From the everyday word 'blossom,' meaning to open out or unfold like a flower. The needle 'fans out' or sweeps through a wide arc as the aircraft crosses over the station, suggesting the opening of a flower.
Why Pilots Care
Confirms the parachute has deployed correctly and will provide the necessary drag to reduce impact speed.
Analogy
It is like a drop of ink spreading on paper: the mark gets wider, but the original drop did not become that large.
Intuition Check
Blossom effect does not mean the target or weather is physically growing. It means the radar display is making the return appear to spread or enlarge.
Example Sentence 1
As we approached the NDB, the needle began to swing widely, and the blossom effect confirmed we had crossed directly overhead.
Example Sentence 2
A delayed blossom effect can increase opening shock and risk of malfunction.