Event: CPT 5
Dynamic rollover - An accelerated roll about a ground pivot
point (landing gear/skids). When AOB or side drift during takeoff or landings
occur, lateral cyclic control becomes sluggish and less effective. If AOB
passes 15°, the helo will enter a roll which can not be stopped
with cyclic. Without lateral trim, aircraft may exceed angle in less than
During slope or crosswind landing and takeoff maneuvers exceeding the critical rollover angle (15o) or exceeding 10o per second will cause the helo to roll over onto its side regardless of cyclic corrections introduced by the pilot.
For dynamic rollover to occur 2 essential elements must exist:
1. Ground pivot point
2. A side force
• Side force is always present due to right tail rotor thrust, which is offset with left cyclic. Left cyclic tilts the lift vector to the side creating a sideward force to balance the thrust from the tail rotor. Critical rollover angle is reduced for a right skid down condition, crosswind, lateral CG offset, and left rudder pedal inputs.
• When landing or taking off, keep aircraft trimmed and do not allow aircraft roll rates to build. If roll rates begin to build recover by smoothly lowering the collective.
• Lowering the collective will eliminate the lift vector and hence the sideward force
• The static roll-over angle for the TH-57 is approximately 31°.
Critical rollover angle is reduced (made worse) for a right skid down condition, cross winds, lateral center-of-gravity offset, and left rudder pedal inputs.
To avoid entering roll, pilot should
1) Maintain trim
2) Not allow aircraft rates from becoming large
3) Not allow aircraft bank angle from becoming too large
4) Fly smoothly
To recover, pilot should use a smooth, moderate collective reduction less than 40% (full up to down in 2 sec). Lowering collective too quickly may cause mast bumping or dynamic roll in the opposite direction.
During slope landings
1) Descend slowly, placing upslope skid down first
2) Lateral cyclic into slope to maintain level TPP
3) Set cyclic to neutral position once assured helo will remain stable
4) Do not land on a slope greater than 7.5 degrees
5) If helo rolls upslope side (5 to 8 degrees of level), collective down
In crosswind maneuvers, hold cyclic into wind and land/takeoff downwind
skid first until firmly on ground.
Static rollover (if aircraft were pushed with no thrust from blades) is 31°.
• With one skid on the ground and thrust approx. equal to weight, if the lateral control becomes sluggish or ineffectual, contacts the lateral stop, or if bank angle or roll rates become excessive (15 degrees or 10 degrees/sec) the aircraft may roll over on its side. Reduce the collective to stop the roll and correct the bank angle to level.
• When landing or taking off, with thrust approx. equal to the weight and one skid on the ground, keep the aircraft trimmed and do not allow aircraft roll rates to build up. Fly the aircraft smoothly off (or onto) the ground, carefully maintaining trim.
Note - Do not attempt to level the skids prior to takeoff/landing as this will aggravate the side drift and possibly lead to dynamic rollover [NATOPS 11.8, AERO 5-8]
1. 2:1 Vibration level increases
2. Pitch-up of the nose (Left blade 270° stalls, due to phase lag the loss of lift is felt over the tail causing the tail to drop and the nose to pitch up)
3. Rolling tendency toward the stalled side (left)
Three factors, during blade stall:
1. Up collective (increased power for forward airspeed-increase blade pitch)
2. Forward Cyclic (increased forward airspeed-causes retreating blade pitch angle to increase)
3. Increased blade flapping due to high airspeed
Factors which increase the potential for blade stall:
High blade loading (i.e. high gross weights / G loading)
Low rotor RPM
High Density Altitude
Factors which affect stall include:
2. Gross Weight
3. Density Altitude
4. G loads
If blade stall is encountered the pilot should:
1. Reduce airspeed (reduces pwr req, reducing pitch/AOA)
2. Decrease collective pitch (reduces AOA)
3. Descend to a lower altitude (decreases pwr req.)
4. Decrease the severity of the maneuver (reduces G loading)
5. Increase rotor rpm (increases rotational velocity)
CAUTION • Entry into severe blade stall can result in structural
damage to the helicopter. [NATOPS 11.9,
1. Forward cyclic to gain airspeed
2. Decrease collective
If impact is imminent:
3. Level aircraft to conform to terrain
Warning • Increase collective has no effect toward recovery and will aggravate vortex ring state. During approaches at less than 40 KIAS, do not exceed 800 feet/min descent rate.
Indications: Uncommanded descent with associated maximum torque, Rotor rpm droop, Possible loss of tail rotor effectiveness
1. Nr - Maintain
2. RPM switch - FULL INCREASE
3. Airspeed - 50 KIAS (min pwr req.)
4. Angle of bank - Level Wings
5. Jettison stores - As Required
If impact is imminent:
6. Level aircraft to conform to terrain
7. Cushion the landing
When the twist grip is full open the pilot may experience:
Indications: Nf indication higher than Nr, Low torque indication, Ng and TOT indications lower than normal and not responsive to collective
2. Twist grip FLIGHT IDLE
If time and altitude permit:
3. Twist grip Smoothly Rotate to Full Open
If Nf/Nr are married:
4. Collective Increase
If sprag clutch continues to slip:
6. Twist grip Closed
If the sprag clutch reengages:
7. Land as soon as possible
CAUTION • After completing the autorotative landing, ensure the twist grip is secured. Failure to do so may result in sudden reengagement of the sprag clutch, causing severe damage to the drive system.
Note • Multiple attempts to reengage the sprag clutch are permitted dependent on time and altitude.
Indications: Nf/Nr married during shutdown, Nf/Nr married above 100% during autorotational flight
1. Ensure twist grip is full open
2. Land as soon as possible
Warning • If suspected during an autorotation, execute a waveoff before Nr decays below 85%.
Note • In a normal autorotation, Nr and Nf may be matched together between 92-96% steady state.
(none for this event)
(none for this event)
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