Question: Which beacon is located 2.5 miles south of Hemel Hempstead, Hertfordshire?
Sentence (from "Bovingdon stack"): Other holding patterns serving Heathrow are at Biggin Hill, Kent (BIG - SE Arrivals), Lambourne, Essex (LAM - NE Arrivals) and Ockham, Surrey (OCK - SW Arrivals), where inbound aircraft will normally use the pattern closest to their arrival route.
Relevant evidence: No