CH-46E STAN MANUAL
CHAPTER 6
TERRAIN FLIGHT
PARAGRAPHPAGE
TERRAIN FLIGHT ...... 6001 6-2
AIRCREW COORDINATION ...... 6002 6-2
COMFORT LEVELS ...... 6003 6-3
INFLIGHT EMERGENCY PROCEDURES ...... 6004 6-3
COMMUNICATION ...... 6005 6-4
TERF MANEUVERS ...... 6006 6-4
LOW LEVEL FLIGHT DEPARTURE ...... 6007 6-5
LOW LEVEL FLIGHT APPROACH ...... 6008 6-6
LOW LEVEL QUICK STOP ...... 6009 6-7
MASKING/UNMASKING ...... 6010 6-8
BUNT ...... 6011 6-8
ROLL ...... 6012 6-9
TURNS ...... 6013 6-10
HAZARDS ...... 6014 6-10
CHAPTER 6
TERRAIN FLIGHT
6001. TERRAIN FLIGHT
1. Terrain Flight (TERF) uses terrain, vegetation, and man made objects to improve survivability by degrading the enemy's ability to visually, optically, or electronically detect, track or fire upon the aircraft. TERF is composed of three basic techniques; low level, contour, and Nap-of-the-Earth (NOE).
a. Low Level Flight. Flight conducted at a selected altitude at which detection or observation of an aircraft, or of points from and to which it is flying, is minimized. The route to be flown is pre-selected and conforms generally to a straight line with a constant airspeed and altitude.
b. Contour Flight. Flight at a lower altitude than low level flight, which conforms generally and in proximity to the contours of the earth's surface. Airspeed and altitude varies as vegetation and obstacles dictate.
c. Nap-of-the-Earth Flight (NOE). Flight as close to the earth's surface as vegetation and obstacles permit, while generally following the contours of the earth. Airspeed and altitude are influenced by the terrain, weather, ambient light and the enemy situation.
d. Regardless of which flight technique is used, there are fundamental considerations, skills and procedures which the assault support helicopter pilot must employ to successfully conduct terrain flight. These fundamentals differ from conventional flight techniques in that terrain flight involves flight close to the earth's surface at speeds varying from a hover to the maximum airspeed.
6002. AIRCREW COORDINATION
1. Terrain flying is a demanding activity requiring precise aircrew coordination and teamwork. The use of aircrew coordination to establish a division of responsibilities and to organize cockpit duties allows safe, effective terrain flight. Specific cockpit duty assignments and responsibilities may vary, depending on the mission, the tactical situation, and the terrain flying techniques employed. Aircrew duties and responsibilities shall be assigned and thoroughly explained by the aircraft commander during the flight brief. The following guidelines will assist in defining aircrew duties and responsibilities for terrain flight operations.
2. Pilot at the Controls. The pilot at the controls (PAC) has two primary responsibilities; controlling the aircraft and avoiding obstacles. The pilot must keep a scan outside the aircraft and avoid distractions, particularly cockpit related distractions that could hinder his external scan. The PAC reports terrain and landmark information to the PNAC to assist in navigation. The PAC retains control of the aircraft during an aircraft emergency and executes those emergency procedures required of the pilot at the controls as set forth in the preflight briefing.
3. Pilot not at the Controls. The pilot not at the controls (PNAC) of the aircraft is primarily responsible for accurate navigation. The PNAC must remain oriented at all times and inform the PAC of the direction to be flown, and of airspeed adjustments for timing. The PNACe assists the PAC by monitoring cockpit instruments, the mechanical functions of the aircraft and the performance of the crewchief and gunners. During an aircraft emergency, the PAC executes those emergency procedures assigned by the instructions set forth in the preflight brief.
4. Crewchief and Gunner/Aerial Observer duties. Crewchiefs and Observers are responsible for monitoring the mechanical functioning of the helicopter. They assist in terrain recognition and keep the aircraft clear of obstacles. Crew members will be positioned where they can best observe their areas of responsibility. Both crewchief and gunner shall be thoroughly briefed on the conduct of the flight, rotor clearance and other coordinating instructions.
6003. COMFORT LEVELS. In initial terrain flight training, the instructor pilot must be aware of the comfort levels of all crewmembers. Comfort level is defined as the lowest altitude at which a crewmember can effectively function without undue apprehension. As the copilot gains more experience and expertise in terrain flying, the pilot’s comfort level should adjust to allow for flights at a lower altitude.
6004. INFLIGHT EMERGENCY PROCEDURES. Crewmember duties and responsibilities concerning emergency procedures must be assigned and thoroughly explained by the aircraft commander during the preflight brief. It is essential that each crewmember know his emergency procedure duties, particularly immediate action items, as reaction time is reduced. Certain practices which may occur regularly in the execution of emergency procedures under normal conditions, such as transferring control of the aircraft, may not be possible and should be addressed in the preflight brief. To sharpen required skills, crewmembers will find that "dry runs" through emergency procedures will help immeasurably.
6005. COMMUNICATION. Terrain flight navigation requires an increased exchange of information among crewmembers. The PNAC must furnish the PAC with short, concise information. The PAC describes obvious terrain features he notices in standardized terms to facilitate understanding. Information should be provided to the PAC in small increments. The pilot should not have to focus his attention inside the cockpit. The PAC should be told to turn right or left to a "clock" position and to a recognizable terrain or vegetation feature. Instructions such as "...turn left, 10 o'clock, fly towards the lone pine" can be used to tell the PAC what to do to follow the desired course. The PAC should not be told to fly a specified airspeed requiring him to look in the cockpit. Rather, the PAC should be told to increase or decrease airspeed relative to the airspeed being currently maintained. Example: "Slow down, I’ll call when your airspeed is good." The PAC can then reduce airspeed without looking at the airspeed indicator.
6006. TERF MANEUVERS.
1. Terrain flight (TERF) is the use of low level flight techniques while operating in the terrain flight tactical environment. In HMM(T)-164, low work maneuvers will be taught to introduce those flight techniques used in low level or contour modes of terrain flight.
2. Prior to commencing TERF maneuvers, a blade walk is conducted to provide a visual reference point for rotor tip path clearance. With the aircraft rotors turning, the crewchief will walk around the rotor arc stopping at the 3, 12, 9, and 6 o'clock positions. This provides the pilots and observers with a visual reference point for rotor tip path clearance.
3. Power checks are used to verify that sufficient power and control of the helicopter exists to safely operate in all phases of the TERF environment under existing ambient conditions.
a. Before flying a mission, the pilot shall perform hover in ground effect (HIGE) and hover out of ground effect (HOGE) performance checks to validate preflight planning. He shall determine the following:
(1) Engine power available equals or exceeds the values specified in the NATOPS flight manual for the ambient conditions.
(2) Sufficient helicopter performance exists about all axes of the helicopter for safe downwind and crosswind operation under existing turbulence and wind conditions.
b. Technique.
(1) HIGE: In a safe hover area stabilize in a 10 to 15 foot hover, check the power required to HIGE. If it is less than or equal to the power required to HIGE computed during the preflight planning, check HIGE power with the aircraft facing downwind. HIGE performance checks shall not be conducted at night unless the mission dictates, and then only at home field or an approved outlying field or site where adequate ground hover reference points exist.
NOTE:
If HIGE computations were based on no wind conditions and the hover area has wind, the power actually required may be less than that computed.
(2) HOGE: Increase the hover altitude to 75 feet and check HOGE power required initially with the aircraft facing into the wind. If power required to HOGE is less than or equal to the power required to HOGE computed during preflight planning, check HOGE power required and aircraft control authority with the aircraft facing downwind. HOGE performance checks shall not be conducted at night unless the mission dictates, and then only at home field, or at an outlying field or site where adequate ground hover reference points exist.
CAUTION:
When the helicopter is at or near maximum gross weight and HOGE is being performed downwind during turbulent or windy conditions, actual power required may increase or exceed power available. HOGE performance checks shall not be conducted when mission gross weights exceed single engine gross weight limitations or exceed maximum gross weight for vertical takeoff from HOGE condition, both of which are determined from the helicopter performance charts in the NATOPS manual.
c. Conclusions. If both HIGE and HOGE power required are equal to or less than computed, continue the mission. Maintenance personnel should be informed of any noticeable degradation in observed engine performance. Always ensure that sufficient power is available to execute a safe landing and/or transition into forward flight.
6007. LOW LEVEL FLIGHT DEPARTURE.
1. An obstacle takeoff is used to clear an obstacle in the departure path of the helicopter. Power available and power required (HOGE) must be carefully computed.
2. Make a vertical takeoff to a hover, stabilize and check torque. Continue to climb vertically eliminating all drift. After gaining sufficient altitude to clear the obstacle (indicated by tip path plane cresting obstacle), apply gradual forward cyclic to transition to forward flight. Too much forward cyclic may produce settling. In zones with dust or debris, do not attempt to stabilize in a hover, transition to forward flight immediately after breaking the deck as long as the aircraft is clear of obstacles.
3. Common errors and safety notes.
a. Failure to maintain heading.
b. Accelerating or climbing too rapidly and applying excess power.
c. Ballooning, failure to maintain a constant angle of climb.
d. Failure to smoothly transition to the terrain flight profile.
6008. LOW LEVEL FLIGHT APPROACH.
1. Allows the pilot to transition for landing from the TERF profile. Additional information on tactical approaches can be found in the CH-46E Tactical Manual (TACMAN).
2. Upon reaching one-half to one KM from the intended point of landing, adjust airspeed to intercept the final approach course in balanced flight while minimizing aircraft signature.
3. Once established on course and on glide slope, reduce power to maintain the desired approach angle and execute a no hover landing if appropriate (glide slope angle should not exceed 45 degrees).
4. Technique. Accurate navigation by the crew is essential for a successful first pass approach.
5. Common errors and safety notes.
a. Early or late landing transition.
b. Failure to maintain proper rate of closure.
c. Excessive airspeed on final.
d. Failure to use a quick stop approach if required.
6009. LOW LEVEL QUICK STOP.
1. A quick stop is performed by rapidly reducing forward airspeed while maintaining a constant altitude and heading. It may be used to transition the aircraft from high speed to a low level approach or for other tactical or safety reasons.
2. The quick stop maneuver is entered at 100 KIAS and 100 feet AGL on runway heading. Stabilize the aircraft on airspeed and altitude. Begin a smooth and gradual flare with aft cyclic simultaneously reducing collective pitch to rotate about the aft tip path plane. In the flare, the pilots should maintain approximately 125 feet on the RADALT. This will ensure that the aft rotor system remains at 100 feet AGL throughout the maneuver. Maintain heading with rudders. If collective movement is not compensated for by aft cyclic, the helicopter will lose altitude. As the aircraft slows, anticipate the requirement for increased collective pitch to prevent settling. As airspeed approaches 35 KIAS, smoothly ease the cyclic forward toward level attitude, and increase collective to avoid loss of altitude. Rapid application of both forward cyclic and increased collective may over stress the aft rotor system. The maneuver is completed by transitioning to forward flight or interception of a glide slope to a landing.
3. Technique.
a. From a stabilized airspeed and altitude, make a coordinated cyclic, then collective movement to initiate flare in which the aft rotor disc is kept at a constant height above the ground so the helicopter rotates, in pitch, about the aft rotor disc. Maintain directional control with the rudder pedals.
b. As the helicopter decelerates to a hover or desired airspeed, allow the nose of the helicopter to descend while continuing to maintain the altitude of the aft rotor disc by power application.
c. Maintain visual reference to the ground throughout the maneuver. Judge the additional height the cockpit must rise to maintain the aft rotor disc at a constant height during the flare.
3. Common errors and safety notes.
a. "Ballooning" the helicopter through a greater altitude change than is necessary when entering the maneuver.
b. Allowing the altitude of the aft rotor disc to settle through the original altitude after the initial "ballooning" on entry.
c. Allowing the heading to drift.
d. Improper cyclic and collective coordination at the termination of the maneuver requiring large power application at the end.
6010. MASKING/UNMASKING.
1. These maneuvers minimize aircraft exposure to enemy observation while affording the friendly helicopter the opportunity to observe terrain along the axis of advance.
2. Technique.
a. Descend vertically to a masked condition using the crewchief to ensure the aft rotor disc of the helicopter is also masked.
b. Move sideways a sufficient distance to see around the obstacle or gain sufficient altitude to see through or above the obstacle. Remain unmasked no more than 10 seconds.
3. Common errors and safety notes.
a. Remaining unmasked for excessive periods of time.
b. Over-exposure due to incorrect terrain interpretation.
c. Allowing the helicopter to drift forward or up slope, thus reducing obstacle clearance and the possibility of re-masking or landing quickly if necessary.
d. Excessive rate of descent.
6011. BUNT.
1. This maneuver enables the pilot to negotiate a terrain obstacle that lies generally perpendicular to his flight path. The bunt specifically allows the pilot to fly over an obstacle in a wings level attitude using a combination of power and cyclic to minimize exposure to enemy visual or electronic detection.
2. Technique.
a. Approaching the obstacle, use power to climb slightly above the approximate height of the highest obstacle by 50 feet.
b. As the obstacle is crossed, the nose is lowered (maintain positive power to the rotor system) to facilitate the descent and to provide terrain clearance for the aft rotor disc. Smooth, slow control movements must be used when pushing the nose over to prevent the unloading of the rotor system. This is the reason positive power must be maintained.
c. As the obstacle is crossed, use power and aft cyclic to control airspeed, maintain obstacle clearance and arrest the rate of descent to level off at the original altitude.
3. Common errors and safety notes.
a. Abrupt and or erratic control movements which cause negative "g" flight and large yaw excursions.
b. Late initiation of maneuver which causes the helicopter to be highlighted above the horizon.
c. Failure to maintain balanced flight.
d. Excessive power
e. Excessive rate of descent.
f. Descending below 50 feet above the highest obstacle.
6012. ROLL.
1. The roll is a maneuver used to cross an obstacle running generally parallel to the intended flight path.
2. Technique.
a. Initiate the maneuver with 50 feet of clearance and with a 45 degree turn toward the obstacle to be crossed and at the same time apply sufficient collective to climb to an altitude just above the obstacle. Maintain power on the rotor system throughout the maneuver to avoid unloading the rotor heads.
b. Cross the obstacle wings level or wing down. Keep the ball centered at all times. If crossing the obstacle wing down, ensure that the rotor tip path is clear of the terrain.
c. Upon cresting the obstacle, return to the original heading while adjusting cyclic and collective to return to the original airspeed and altitude.
3. Common errors and safety notes.
a. Allowing the rotor tip path to dip too low while close to obstacles.
b. Abrupt or erratic control movements which cause negative "g" flight or large yaw excursions.
6013. TURNS.
1. The technique discussed here ensures adequate terrain clearance during turns in the terrain flight environment.
2. Technique.
a. As the turn is initiated, climb slightly so that the rotor tip path on the inside of the turn does not dip below a planned minimum height of 50 feet above the highest obstacle. Turns in excess of 30 degrees angle of bank make the rotor tip path the lowest portion of the helicopter during the turn.
b. As the helicopter rolls out of the turn, return to the original altitude.
3. Common errors and safety notes.
a. Allowing the rotor tip path to dip too low while in turns close to obstacles.
b. Failure to return to the original altitude upon completion of the turn.
6014. HAZARDS. As a result of reduced reaction time and the low altitudes associated with TERF, the pilot must contend with a number of hazards, such as wires, birds, low sun angles and other aircraft. The most important factor in avoiding these hazards is for the pilot at the controls to exercise an active external scan at all times. Consider the effects of low sun angles on the vision of the aircrew when planning the mission. Ensure that the visors and windscreen are clean. Prior preparation, an active external scan and solid aircrew coordination are critical to the safe conduct of terrain flight.
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