What is the role of the altimeter setting and QNH in Longitude 700 operations?

• A. Set correct altimeter to ensure altitude accuracy; cross-check with field elevation and approach procedures.
• B. Altimeter setting is optional.
• C. Ignore altimeter and rely on GPS altitude.
• D. Set to 29.92 only.

Answer: (A)

Setting the local altimeter to the correct QNH makes the instrument read your true altitude above mean sea level, which is essential for accurate terrain clearance and for following published altitude steps on procedures. In Longitude 700 operations, you must verify that the altimeter shows the altitude that corresponds to field elevation and the charted approach/altitude constraints, so you can safely execute climbs, descents, and approaches. GPS altitude can be misleading for instrument procedures, and 29.92 is used only when flying above the transition altitude in standard pressure, not for normal terminal operations. So you set the local QNH and cross-check with the field elevation and approach procedures.