Possible Clues:

• Entrance with an axis
• It comes full circle as you work your way through 20-, 36-, 43- and 58-Across
• Turning letter in and out
• A roundabout means of gaining admission
• Frequent personnel change
• Situation with high personnel turnover
• A roundabout way in this
• 16-Across can slam a ___
• Office entryway, and what you must pass through to solve 18-, 23-, 53-, and 61-Across
• Job position in which no one lasts long