What is indicated by the lightning bolt symbol on an approach chart?

The lightning bolt symbol on an approach chart is used to indicate the glide slope intercept point of an Instrument Landing System (ILS) approach. This is the point at which the aircraft should intercept the glide slope, which is a critical component in ensuring a safe descent profile towards the runway. Pilots utilize this information to align their approach with both the lateral and vertical guidance provided by the ILS, leading to more accurate landings.

While the other choices relate to other aspects of instrument approaches, they do not accurately describe what the lightning bolt symbol signifies. Understanding the glide slope intercept is essential for pilots as it helps them maintain the correct path during descents and approach phases, providing a safe and reliable way to land in various weather conditions.