LIMIT
Condition : LIMIT refers to N1, N2 or EGT approaching or exceeding its respective limits. However, if the ENG OVERHEAT amber light or ENGINE FIRE switch illuminates, the respective NNC must be accomplished.
Never retard the thrust lever during takeoff run in an attempt to control the engine exceedance !
The recall item of the NNC [Engine Limit or Surge or Stall] must never be executed during takeoff run, unless it is decided to abort the takeoff procedure !
Delay the recall items until airspeed and altitude (with a minimum of 400 feet AGL) are adequate to control the airplane and to clear obstacles on the departure route.
If an engine limit has been exceeded and no apparent damage is observed, the flight may continue to the planned destination, but anyhow an Air Safety Report (TFIR) must be filed upon the first arrival and the aircraft will be grounded until the TFIR is cleared.
SURGE
Condition : SURGE is a breakdown of airflow in the compressor, causing the airflow to return to the front of the engine. Surge is recognized by abnormal N1 fan speed values, N1 oscillations, sudden different N1 values between both engines with equal throttle setting and/or no response to thrust lever.
Surge is typically causedby internal engine damage (compressor blade fracture, bird strike) and internal tip clearance changes. Low altitude and high power settings produce the loudest surge noise (bangs), while high altitude engine surgecauses a muffled noise and light vibration.
Engine response to a loss of engine thrust control varies from engine to engine to engine, such as fixed RPM, engine shutdown, operation at low RPM or any other case whereby the affected engine does not respond to thrust lever movement. While it is common for EGT to reach or exceed limits during engine surge, EGT rise may go unnoticed.
Selecting takeoff thrust in heavy crosswind or tailwind conditions at aircraft standstill increases the chance of engine surge on takeoff. A rolling takeoff is recommended.
Refer to FCTM 8.x [Loss of Engine Thrust Control] for additional information.
STALL
Condition : STALL can be recognized by loud engine noise (“bangs”), fluctuating RPM, possible increasing EGT, engine vibrations and some aircraft yaw.
Engine stall can be caused by FOD, by off schedule VSV or by disrupted airflow.
The following actions may help in getting the engine out of a stall condition :
- retarding the thrust lever
- selecting the associated A/C pack in HIGH
- selecting engine anti-ice and wing anti-ice ON (TAT < 38 degrees C / 100 degrees F)