Aviation LAB

On all jet engines, but particularly on high bypass ratio engines, the engine acceleration profile is not linear. It follows the engine control law that is defined to optimize the acceleration in a way that the risk of engine stall is reduced. It also takes into account the influence of the position of the engine installed on the aircraft and the effect on the airflow at the engine’s inlet due to its proximity to the ground and the surrounding aircraft structure. Every engine has its own performance level due to manufacturing tolerances. In addition, engine performance evolves with time due to wear and ageing. As a consequence, the acceleration profiles may slightly differ from one engine to another on an aircraft, even if fitted with new engines. Similarly, the idle thrust can slightly differ from one engine to the other. Taking into consideration both of these parameters, if the Flight crew applies the takeoff thrust directly from idle thrust, without doing any stabilization step, the difference in engine acceleration performance could cause a strong asymmetric thrust condition that could be difficult to counteract with nose wheel steering only, due to limited effectivity of the rudder at low speed. The stabilization step ensures that all engines reach a rotation speed value from where the increase of engine thrust will be almost identical to each other. The N1/EPR/THR stabilization value is defined during flight test campaign for every engine type with collaboration from engine manufacturers. Using a stabilization step, the potential thrust asymmetry remains limited before the stabilization and both engines accelerate almost simultaneously. Specific use-case when differential thrust is used for the aircraft line-up In some cases, differential thrust is used to line-up the aircraft on the runway. If the pilot commands takeoff power without first doing the engine thrust stabilization step, the resulting asymmetric thrust condition may be significant due the engines accelerating from an already very different rotation speed. This is why a thrust stabilization step is important after using differential thrust to line-up the aircraft, to avoid causing a strong thrust asymmetry condition during the early stages of the takeoff roll. Source: Airbus Safety First

VS: Stalling Speed For a conventional aircraft (not Airbus), the reference stall speed is based on a load factor that is less than 1g. This gives a Stall Speed that is lower than the stall speed at 1g (1 Gravity). See Figure B6. All operating speeds are expressed as functions of this speed (for example, VREF = 1.3 VS). VREF: Reference speed, It's the steady landing approach speed required at a height of 50 feet above runway threshold for a defined landing configuration. It's used as a reference for calculating the final approach speed and the landing distance. Coefficient of Lift Vs Angle of Attack Because the A320 family aircrafts has a low speed protection feature that the flight crew can't override, (This is true meanwhile the aircraft remains in Normal Law) Airworthiness Authorities have reconsidered the definition of stall speed for the A320. All the operating speeds must be referenced to a speed that can be demostrated by flight tests. This speed is designated VS1g (Stall Speed at 1 Gravity). Coefficient of Lift Against Speeds Representation during A320 Normal Law High Angle of Attack Protection Airworthiness Authorities have agreed that a factor of 0.94 represents the relationship between VS1g for A320 Family Aircraft and VS for conventional aircrafts. As a result, Authorities allow A320 family aircraft to use the following factor: VREF = 1.3 x 0.94 VS1g = 1.23 VS1g As a conclusion every time we refered to the stall speed on A320 family aircraft we use VS1g instead of VS. If you like this information please comment ans share!!!

One common false assumption in Aviation is that errors and violations are limited to incidents and accidents. Recent data from Flight Operations Monitoring (e.g. LOSA) indicate that errors and violations are quite common in flight operations. According to the University of Texas LOSA database: • In around 60% of the flights at least one error or violation was observed, the average per flight being 1.5. • A quarter of the errors and violations were mismanaged or had consequences (an undesired aircraft state or an additional error). • A third of the errors were detected and corrected by the flight crew, 4% were detected but made worse, and over 60% of errors remained undetected. This data should underline the fact that errors are normal in flight operations and that, as such, they are usually not immediately dangerous. According to ICAO the Threat and Error Management (TEM) framework is a conceptual model that assists in understanding, from an operational perspective, the inter-relationship between safety and human performance in dynamic and challenging operational contexts. As aviation industry members we must implement a process of detecting and responding to threats and errors to ensure that the ensuing outcome is not an error, further error or undesired state. University of Texas TEM Model defined A Threat as an event (in relation to the environment or the aircraft) or an error (from another aircraft, air traffic control or maintenance) occurring outside the influence of the flight crew (not caused by the flight crew). It increases the operational complexity of a flight and requires crew attention and management if safety margins are to be maintained. Environmental Threats - Adverse Weather - Airport Conditions - Terrain - Other Traffic - ATC requirements and/or Errors. Operational Threats - Operational Pressure - Aircraft Malfunctions - Maintenance Error - Ground handling Error - Cabin Events - Crew Scheduling Errors. Latent Threats - Systematic or Organisational deficiencies - Hardware Design - Training deficiencies - ATC systematic deficiencies. Other Threats Stress - Fatigue - Distractions. Accordingly to the TEM Model a Flight Crew Error is defined as an action or inaction that leads to a deviation from crew or organisational intentions or expectations. Error in the operational context is considered as a factor reducing the margin of safety and increasing the probability of adverse events. The University of Texas defines the following Types of Errors: • Intentional non-compliance errors (violations): intentional and conscious violations of SOPs or regulations, including shortcuts or omission of required briefings or checklists. • Procedural errors: errors including slips,lapses or mistakes in the execution of regulations or procedures. The intention is correct but the execution is flawed. • Communication errors: occurs when information is incorrectly transmitted or interpreted within the cockpit crew or between the cockpit crew and external sources such as air traffic control. • Proficiency errors (skills errors): indicate a lack of knowledge or stick and rudder skill. • Operational decision errors: discretionary decisions not covered by regulation and procedure that unnecessarily increases risk. Examples include extreme manoeuvres on approach, choosing to fly into adverse weather, or over- reliance on automation. Is a fact that Threats and Errors will affect the safety of any flight even more because of: • Weaknesses in training and knowledge, • Lack of strategies of threat detection and management, • Insufficient or ineffective strategies of potential error detection, • Ineffective strategies of error recovery or management, • Ineffective strategies of undesired states recovery or management, A Trained Pilot is a Safe Pilot!!! References: ICAO: Threat and Error Management (TEM) in Air Traffic Control Approved by the Secretary General and published under his authority If you like this information please comment and share!!!