This next lot of quotes from a recent LSO NATOPS MANUAL found online is perhaps again sometimes not relevant to the initial question but 'context' is required. I would encourage any interested to download these PDFs to see the text in context with many excellent illustrations (only some may be shown in this thread - if any). Enjoy.
NATOPS LANDING SIGNAL OFFICER MANUAL 17 June 2004
http://www.vaw120.navy.mil/NATOPS/UE_Instructions/LSO%20NATOPS.pdf (2Mb)
4.2.5 Stabilization ModesThe position of the SOT assemblies for any given ship’s pitch, roll and heave is calculated from a series of stabilization equations in the stabilization software. The result is a stabilized glideslope with respect to the horizon under moving deck conditions. The following modes of IFLOLS stabilization are employed.
4.2.5.1 Inertial Mode Of StabilizationThe Primary mode of operation for the IFLOLS. This Mode is line stabilization with additional correction for ship’s heave motion. It essentially stabilizes the glideslope regardless of carrier motion. The pilot must be on the centerline of the angle to see a properly stabilized display. During heavy sea states (5/6) in inertial mode, the hook to ramp clearance and touchdown point indicators will occasionally display a negative or aft touchdown point respectively.
The dynamic touchdown point varies more in inertial mode than it does in line mode. This is the sacrifice for a more stable light beam/glideslope for the pilots. A pilot on a perfect pass may hit any of the four wires, the ramp or bolter, depending on ramp motion and heave. At the moment of touchdown, the hook touchdown point will be displayed by the dynamic hook touchdown point indicator for a centered ball pass.
4.2.5.2 Line StabilizationUsed as a backup to inertial mode, this mode stabilizes the IFLOLS display for pitch and roll motions of the ship maintaining a predetermined line in space at the intersection of the IFLOLS light plane and the true vertical plane through the centerline of the angled deck (Figure 4-5). This provides a completely stabilized glideslope referenced to the carrier deck, (glideslope moves with deck heave motion) as long as the pilot is on centerline of angled deck.
Line mode is not stabilized for ship’s heave(vertical displacement). Pilot perceived ball movement is because of ship’s heave. Mode 1 should be flown using line stabilization mode, inertial is acceptable. IFLOLS Line mode should be used when aircraft are landing using ACLS Mode I. The aircraft chases the deck in Mode I approaches. For Mode I approaches IFLOLS Line mode provides a steadier ball to the pilot than inertial. With moderate and higher ship motion the pilot will still see some ball motion in the situation. Inertial mode should be used for ACLS Mode IA, II, III and all other approaches.
4.2.5.3 Stabilization LimitsLens stabilization limits for the MK 13 MOD 0 are ±1.62 pitch, ±8.19 roll. It should be noted that in any discussion of deck motion and its associated effect on IFLOLS, rate of pitch is just as important as amount of pitch. A moderate amount of pitch, normally within the stabilization capability of the IFLOLS, can result in an unstabilized glideslope if the rate is rapid enough. The ballscrew assemblies simply cannot move to the required position quickly enough when the deck excursions are rapid.
4.2.6 Effects of Deck MotionUsing basic geometry, each 1-foot aircraft vertical deviation from optimum glideslope moves the hook touchdown point forward or aft in the landing area by the following distances:
Basic Glideslope Angle Distance in Feet
3 19.1
3.5 16.4
3.75 15.3
4 14.3
4.2.7 Effective Glideslope Due to Wind and Deck MotionThe glideslope angle, referred to as the Basic Angle (BA) aboard ship, is the fixed pitch angle around which the lens assembly stabilizes. A BA setting of 3.5 is most commonly used, with 4 used for higher wind-over-deck conditions (38+ knots) or on the small decks when Hook-to-Ramp (H/R) clearance is near the 10-foot minimum. In moderate wind-over-deck conditions (32 to 37 knots), a 3.75 BA may be desirable. In Figure 4-6, note that decreased closure rate of aircraft to ship caused by wind-over-deck reduces the actual glideslope flown (effective glideslope).
WIND OVER DECK (KNOTS) BASIC ANGLE (DEGREES) EFFECTIVE GLIDESLOPE*
35 4 3.2
30 3.5 2.8
*Based on a 130-knot approach speed
Aircraft landing stress limits are predicated on moderate deck conditions. Extreme deck motion may significantly increase these landing stresses; the ramp coming up at touchdown increases relative sink rate. Additionally, 1 of ramp down is the same as adding 1 to the glideslope as far as aircraft landing stresses are concerned. These deck motion factors are among the most critical to consider when landing aircraft on carriers.
During pitching deck conditions the aircraft hook may not engage the crossdeck pendant at the optimum angle. This may result in an apparent increase in the frequency of hook-skip bolters.
4.2.8 Roll Angle and Hook-to-EyeIFLOLS Unit 1 has 12 light tables, one behind each lens (cell). These light tables are moved in unison to stabilize the source light plane for ship motion and to change the Basic Angle (BA) and set different aircraft Hook-to-Eye (H/E) values. To accomplish this the source light plane is rotated about two horizontal axes at right angles to each other, one axis called lens pitch and the second axis lens roll. While the IFLOLS Unit 1 does not have an actual pitch and roll axis, the source light plane rotates as if both axes were located within Unit 1. The lens pitch axis is perpendicular to the angle deck centerline and the lens roll axis is parallel to the angle deck centerline. The tilt in pitch, referred to as the basic angle, is seldom changed during a recovery. Typical basic angles are 3.5 or 4.0. See Figures 4-7 and 4-8.
Rolling (rotating) the source light plane, on the lens roll axis, causes the glideslope along the centerline of the landing area to be raised or lowered. This compensates for the various H/E distances to provide a constant hook path for all aircraft (Figure 4-9). H/E distance, which varies between aircraft types, is the vertical distance between the hook path and the pilot’s eye path relative to the carrier (see Figure 4-10). Aircraft Recovery Bulletin No. 62-12 provides H/E values for all aircraft and aircraft configurations. These H/E values, along with BA, desired hook touchdown point, and ship’s static pitch/roll miss trim, are used by IFLOLS to calculate and set the proper static lens roll angle. The static roll angle range of IFLOLS is approximately 8. Static roll changes do not account for stabilization of the source light plane for ships motion. A 0 roll angle is a source light plane that is level in roll. Increasing the roll angle raises the source light plane along the angle deck centerline. The roll angle is increased when changing from an aircraft with a small H/E to an aircraft with a larger H/E. Positive roll angles are roll angles that raise the source light plane above level over the angle deck centerline. For IFLOLS on 68 class carriers a H/E of approximately 16.5 feet with a 3.5 BA and 230 ft HTD results in a source light plane level in roll (zero roll angle). The static roll angles of current fleet aircraft (April 2007) vary approximately 1.5 except for the T-45 which has an approximate −3 roll angle.
For the CVN-76/77, 3 wires HTD 212 ft, the nominal roll angles are all approximately 0.75 more negative with respect to 4 wire 230 ft HTD ships. The CVN-78 will be approximately 1.5 more negative. The selected BA will not change when the lens roll angle is increased or decreased.
CAUTIONBecause of roll angle pilots observing a center ball, but flying an extreme
off-center approach, may have hazardous hook to ramp clearance.
No roll angle or BA settings are used for MOVLAS as the LSO manually controls the ball to establish the proper glideslope. Most field optical landing systems change only basic angle (3.0 or 3.25); no roll angle adjustments are made, and each aircraft type will have a different touchdown point based on its H/E value.
All published lens settings are intended to provide optimum hook glidepath, with a hook touchdown point halfway between the number two and three crossdeck pendants (4 wire ships). Roll angle places the visual glideslope some distance above the hook glideslope that corresponds to each aircraft’s H/E distance. H/E (in feet) is determined for each aircraft while properly configured; flying on speed, optimum attitude, and with a centered ball. For many aircraft, a change in configuration will change H/E distance. H/E values for various configurations are specified in the Recovery Bulletins. If no preconfigured H/E pushbutton is available for the aircraft, IFLOLS has a Non-Standard H/E adjustment to provide the desired glidepath and hook touchdown point.
Failure to maintain optimum aircraft attitude to touchdown may result in engagement of other than the targeted wire even with the aircraft on the visual glideslope (i.e., pilot sees a centered ball) at touchdown. Additionally, pilots flying an optimum aircraft attitude and on a centered ball may also engage other than the targeted wire if there is appreciable ship motion.Deck centerline camber (i.e., the centerline is higher than the deck edge) is for water drainage. On most decks it is approximately 4 inches. All lens settings in the Recovery Bulletins compensate for deck camber.
4.3 IFLOLS STABLIZATION INPUTSIFLOLS receives ship’s pitch and roll information from either the ship’s gyros or SPN-46. IFLOLS receives ship’s heave information from either an IFLOLS generated ship’s heave signal or SPN-46. The IFLOLS signal is generated using the IFLOLS unit 5 accelerometer. The IFLOLS can use either ship’s pitch and roll gyro source with either heave source. When aircraft are landing using ACLS, any mode, IFLOLS should use the same stabilization inputs as SPN-46. Typically SPN-46, SPN-41, and IFLOLS will all use the SPN-46 gyro for pitch, roll, and heave information when aircraft are landing using ACLS.
7.3.7 Excessive Deck MotionThe decision to continue flight operations during periods of excessive deck motion must be made after considering many factors. These factors include but are not limited to the following: amount and rate of pitch, associated heave and roll, day or night, visibility and horizon, air wing and LSO proficiency, tanker and divert availability. Although there are no hard and fast numbers to define excessive motion, as a general rule, deck motion in excess of 20 feet of pitch in anything less than 5 seconds of periodicity should be viewed as an emergency situation. MOVLAS is the primary method of recovering aircraft during excessive deck motion, depending on other factors previously mentioned. LSO workload will be very high in these conditions. The LSO will most likely be required to make nearly continuous voice transmissions during pitching deck operations regardless of whether MOVLAS or IFLOLS is utilized. The LSO will most likely be required to utilize a steeper than normal glideslope as well as to ensure adequate hook-to-ramp clearance during extreme pitch cycles.
CHAPTER 8 Extreme Weather Condition Operations
8.1 DECK MOTIONThe decision to conduct flight operations during periods of excessive deck motion must be made after considering many factors. These factors include, but are not limited to the following:
1. Operational necessity
2. Day or night
3. VMC or IMC
4. Amount and rate of pitch, roll, and/or heave
5. Visibility and horizon
6. Air Wing pilot and Staff LSO proficiency
7. Tanker and divert availability
Any number of these factors can combine to create a wide spectrum of operational risk. Measuring operational risk can be difficult, and there are no hard and fast numbers that define “excessive deck motion.”
The staff LSO, in conjunction with the Air Officer, shall inform the CV/N Commanding Officer when pitching deck limits are exceeded. The decision to continue flight operations will lie at the discretion of the Commanding Officer.
Flight operations with ramp movement exceeding 20 feet total is extremely hazardous. Flight operations in these conditions should be avoided.
Flight operations should not be conducted with deck movement in excess of 35 feet total due to zero hook to ramp clearance with the 4.0 degree glide slope.
Recovery of fixed wing aircraft with a pitching deck significantly increases the risk of hard landings, ramp strikes, off-center engagements and in-extremis low fuel states airborne due to the inherent decrease in overall boarding rate.
Note
The presence of dutch roll increases the risk associated with the recovery of fixed wing aircraft when compared to pure pitch, and should be taken into careful consideration prior to conducting flight operations.
8.1.1 Flight Operations in Pitching DeckWhen deck motion exceeds the stabilization capabilities of the IFLOLS as determined by the Staff LSO (approximately 8 feet of total deck movement in less that 4 seconds), utilization of MOVLAS should be considered for fixed wing aircraft recovery. If the deck is steady for extended periods between deck swings consideration should be given to leaving the IFLOLS rigged and utilize LSO talk-downs during deck swings. This will maximize boarding rates.
Note
IFLOLS Stabilization capabilities are approximate and may vary depending on CV/N.
8.4 EXCESSIVE DECK MOTIONRecovery operations under conditions of excessive deck motion are discussed in Chapter 7 of this manual.
8.5 EXCESSIVE WIND-OVER-DECK OPERATIONSTurbulence and ramp burble increase significantly with RHW values in excess of optimum, resulting in an increased frequency of high landing gear loading.
Excessive crosswinds adversely affect recovery operations. If the recovery crosswinds exceed 7 knots, rates of descent 3 to 6 feet per second in excess of those experienced during normal operations can be expected, even with corrective pilot technique.
Shipboard aircraft recovery operations with recovery crosswinds in excess of 7 knots require the approval of the CV/N commanding officer.
