user: Question: What is the Tenure of the Officer who died in a Helicopter accident with Badge/Serial Number 16805?
Columns: ['Rank', 'Badge/Serial Number', 'Tenure', 'Date of death', 'Cause of death']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['City Marshal', '—', '—', '1853', 'Gunfire']
SQL:

assistant: SELECT "Tenure" FROM "Table" WHERE "Cause of death" = 'Helicopter accident' AND "Badge/Serial Number" = '16805';