Deviating speed and altitude indications, Boeing 737-800NG, OO-JAV, Amsterdam Airport Schiphol
During the climb a difference between the captain's and co-pilot's altitude and speed instruments was noticed. At cruising altitude this difference had increased. The crew attempted to solve the problem, however, this was unsuccessful. A decision was made to return to Schiphol, where the aeroplane made a safe landing.
The Dutch Safety Board emphasizes that standard maintenance procedures or approved alternate procedures
must be followed. In this way, the safety operation of aircraft is ensured.
The incorrect working of the pitot static system causes the presented airspeed and altitude information to become unreliable. These unreliable indications may cause difficulties for the pilots to safely control the aircraft. When these unreliable indications are combined with unfavourable environmental conditions such as cloud layers, the unsafe situation may worsen because pilots are not be able to use outside references -horizon- to aid in controlling the aircraft. During this occurrence the pilots were able to safely fly the aircraft, despite a cloud layer that was present for the majority of the flight. Nevertheless, pitot static system malfunctions have led to serious incidents and accidents in the past.
It is therefore emphasized that maintenance and flight crews must verify that the pitot static system is clear of covers, placards or tape during inspections and preparation for flight to ensure the safety of flight. The operator and maintenance organizations both performed an investigation into the occurrence and shared their findings with the Dutch Safety Board. The Dutch Safety Board used the information from these reports and conducted interviews for this investigation.
More about this incident can be found in the Quarterly Aviation Report Q3 2021.
