Radar altimeter?

quicksilver · by **quicksilver** » 11 Apr 2019, 23:21

...illustrating the importance of what altitude one sets the warning at, and how one is trained to react to said warning. When one’s training habits condition one to all but ignore the warning, the first link in the mishap chain has often been established.

I had the good fortune of learning this before I busted my a$$. The lesson came at night racing around on nvgs at very low altitude; post-flight HUD video review highlighted that I was getting way, way, way too comfortable with what I was doing. Routine disregard of ralt warning was part of the problem.

outlaw162 · by **outlaw162** » 12 Apr 2019, 01:11

This 'suspicion' never seen in any JPALS material I have. Do you have a source for your "'spect" and why would it be necessary. JPALS for one thing guides the F-35C to precision arrested landing on a moving carrier deck via relative GPS.

An autopilot is typically desensitized at various points on the approach profile based on RadAlt to prevent overly aggressive control inputs in close. Nothing to do with JPALS accuracy from a locally augmented differential GPS on a pitching deck as such....it is an autopilot feature, not a JPALS feature, so probably best researched in the auto-flight section of the flight manual, not in documentation material about JPALS. That's why I said I 'spect the RadAlt is tied in with the steering commands because I don't possess an F-35 flight manual.

However, early in the GPS approach game in the 90s, I have flown a number of what used to be called LAAS approaches in an actual aircraft (727) both manually and on autopilot. That auto-pilot was desensitized on a RadAlt schedule, the pilot is not. I can only suspect it would be reasonable to apply the concept (whether RadAlt based or not) to other aircraft auto-pilots to preclude excessive gyrations in close.

spazsinbad · by **spazsinbad** » 12 Apr 2019, 01:14

'outlaw162' I fail to see how a commercial aircraft equates to a naval aviation aircraft on an approach. I could research Naval Aircraft NATOPS however from past reading of such (without looking for this particular info) I don't believe RADALT is used for an auto carrier approach. If someone wants to find that info in a NATOPS before I do feel free to get to it.

outlaw162 · by **outlaw162** » 12 Apr 2019, 01:27

I don't believe RADALT is used for an auto carrier approach.

Is a belief similar to a 'spect?

spazsinbad · by **spazsinbad** » 12 Apr 2019, 01:27

quicksilver wrote:...illustrating the importance of what altitude one sets the warning at, and how one is trained to react to said warning. When one’s training habits condition one to all but ignore the warning, the first link in the mishap chain has often been established.

I had the good fortune of learning this before I busted my a$$. The lesson came at night racing around on nvgs at very low altitude; post-flight HUD video review highlighted that I was getting way, way, way too comfortable with what I was doing. Routine disregard of ralt warning was part of the problem.

Not sure which aircraft you are flying in this anecdote about "...night racing around on nvgs at very low altitude; post-flight HUD video review...". This is not something I did in an A4G in the early 1970s. No NVG; No HUD with video etc. The A4G did not even have the standard A-4F USN avionics. It was very basic but capable avionics-wise. We did not low level at night. The lowest straight and level I experienced would have been in circuits at 1,000 feet. One of my scariest experiences was attempting to listen to the LSO under A4G training (he was an experienced S2E pilot/LSO) debriefing my first deck touch and go at night whilst I was instrument flying downwind at 1,000 ASL waiting for pickup by CCA for my second (rampstrike) touch and go. I basically had to ignore him whilst I did my first task of flying accurately downwind in that inky blackness fully aware the GREAT OGGIN was just below. Apart from going out there that first night this was the first time I had been in this situation. I might stress the A-4 instruments were superb compared to what I flew previously with the WWII era Vampire/Sea Venom catastrophic combo (explained in earlier threads elsewhere). As for the debrief after the 'second' approach - there was none. That LSO did not speak to me again. :roll:

Although the supervising A4G LSO was there he said nothing about it either but he did speak to me.

Must explain that the two LSOs remained on MELBOURNE whilst I cooled my heels ashore for a few days etc. So there was no chance to debrief & after awhile it was futile.

Previously I have on other thread told stories about the old instruments in older aircraft. The ABBAJABBA (artificial horizon) in the A-4 was fantastic, it rarely toppled. During daytime there was no need for me to listen for the RADALT - if low level my eyes were out of the cockpit looking at what to avoid. AS I've said before - if I was lower than the Wandering Albatross I was in deep doo-doo - not long for this world. :mrgreen:

spazsinbad · by **spazsinbad** » 12 Apr 2019, 01:30

outlaw162 wrote:
I don't believe RADALT is used for an auto carrier approach.

Is a belief similar to a 'spect?

You used the word so you would have to tell me. :doh:

quicksilver · by **quicksilver** » 12 Apr 2019, 02:22

Which aircraft on NVGs? Harrier (Night Attack; GR7/9)

Wonderful cockpit layout/lighting/functionality, specifically designed for night attack. Several different types of nvgs, navflir w wide fov raster HUD. Jet has been around in a couple versions since very late 1989/early 1990.

Gums · by **Gums** » 12 Apr 2019, 03:28

Salute!

Outlaw has a point.

You integrate all the data and such, then make a decision.

On our Bobbin SAR at Than Hoa in Dec 1972, Arnie used our projected map and nav position to find a valley to get the Jolly below the clouds. He flew over the valley and watched the radar altimeter. walla! So he dived down and came up to lead the Jolly toward the survivors.

My experience with the SLUF radar altimeter gave me confidence. I don't know how the beam was shaped, but the sucker agreed with my visual and baro altitude right off the runway at The Beach regardless of sea state. On some of our really low, low route landfalls going feet dry, the mist from the water and fog made the radar altimeter a nice thing to have.

Gums sends...

spazsinbad · by **spazsinbad** » 12 Apr 2019, 04:09

Interesting 'Gums' - I guess we are shaped by our experiences rightly or wrongly. However different equipment in different eras and such can differentiate a lot of that experience. For example I don't think anyone ever briefed or called for the RADALT in the A4G to be used; however certainly the Air Warfare Instructors wanted them switched OFF as I mentioned.

Gums · by **Gums** » 12 Apr 2019, 16:06

Here There Be Dragons.pdf: Dragons; (22.89 KiB) Downloaded 771 times

: lighter; dragon-lighter.JPG (128.96 KiB) Viewed 17511 times

Salute!

We did a lotta crazy things, Spaz. But as the avionics got cosmic, they became fairly normal, but still :"challenging" tactics. And the SLUF led the way for the single seat folks. The TF radar mode also had a cross-scan mode with regular gound map, and every other sweep it would do the vertical sweep, then back to PPI. This was in 1971, folks!

An example of how stupid we were in 'nam back in '68, I attach a war story from our association's book on the Dragonfly. So imagine flying down among the hills to drop linear CBU at 400 or 500 feet. We preferred no flares and at least a half of a moon. The big thing we had going for us at Pleiku was we flew the same area of the Trail almost every afternoon and knew all the "gotchya's" We also looked ahead to see if any stars were disapperaing, heh heh.

I never flew with NVG's before I moved on. The guys that did the testing on LANTIRN thot the neat, wide HUD was lots better than goggles.

Gums sends..

steve2267 · by **steve2267** » 13 Apr 2019, 03:57

Great story, Gums. Thx.

outlaw162 · by **outlaw162** » 13 Apr 2019, 17:54

I fail to see how a commercial aircraft equates to a naval aviation aircraft on an approach.

Do a search on LM's CAT-Bird.

BTW, early autopilots were desensitized on coupled approaches based on a timer started after glide-slope capture....with the F-35's digital efcs, variable gains and auto-land capability, who knows what magic ways this could be accomplished?

spazsinbad · by **spazsinbad** » 13 Apr 2019, 21:14

So the CATbird made JPALS test carrier approaches with a high wave-off - so what. Please provide references for your other 'auto-pilot timer decouple less sensitive whatevers' approaches. Are these carrier approaches? It is explained clearly how the F-35C will precisely auto-land with JPALS, please read my PDF for that information. Thanks.

This is latest PDF about JPALS on appropriate thread: download/file.php?id=29793
JPALS Info pp113 10mar2019 PRN.pdf (6.1Mb)

Searching for my 'auto-land' material I see some of it is NOT in this JPALS pdf above. Link to story is (in JPALS thread?):

Look! No Hands
10 Jul 2011 Tommy H. Thomason

"...Part of the interval between the successful demonstration at Bell and the first landing aboard a carrier was dedicated to developing a ship-motion compensation capability. During the last 12 seconds before the touchdown, ship motion was included in the computations; a second or two from touchdown, the corrections to the autopilot ceased and it simply maintained pitch and bank.

A production contract was finally awarded to Bell in March 1960 for the SPN-10 ACLS. NATC accomplished the first fully automated landings with the production system in June 1963 on Midway with an F-4 Phantom and an F-8 Crusader, modified for the capability....

...When the system was working, the performance was brilliant, the airplane coming down the glide slope toward a three-wire arrestment like it was on rails. As might be expected from the vacuum-tube-based technology of the time, however, reliability proved to be a problem. A field change was made to improve SPN-10 reliability but at the expense of its automatic touchdown capability: the pilot had to take over at weather minimums and make the final corrections before touchdown.

In 1966, Bell received a contract to "digitize" the system with solid state electronics and computers and restore full functionality. The redesigned system was designated the SPN-42. A subsequent improvement, the SPN-42A, incorporated an X-Band radar for better system performance in heavy precipitation. It was operationally approved in 1968.

Development of the next ACLS generation, the SPN-46, was begun in 1980 to take advantage of advancements in gyro, computer, and radar technology. It was declared operational in 1987 after an operational evaluation involving Kennedy and F-14s. It is being continually improved but will eventually be replaced by a GPS-based system being developed as a joint service program, JPALS (Joint Precision Approach and Landing System).""

Source: http://thanlont.blogspot.com.au/2011/07 ... hands.html

spazsinbad · by **spazsinbad** » 14 Apr 2019, 01:34

For whatever reason 'outlaw162' has been on about 'JPALS' and how it works since June 2010: viewtopic.php?f=22&t=14115&p=176548&hilit=LAAS#p176548 again: viewtopic.php?f=22&t=14115&p=176657&hilit=LAAS#p176657 also: viewtopic.php?f=55&t=14388&p=183628&hilit=LAAS#p183628 2011: viewtopic.php?f=22&t=14115&p=203975&hilit=LAAS#p203975 again: viewtopic.php?f=22&t=14115&p=204043&hilit=LAAS#p204043

WOT I DUN was searched on LAAS

Now worth quoting: viewtopic.php?f=22&t=14115&p=204057&hilit=LAAS#p204057

A Robust GPS/INS Kinematic Integrity Algorithm for Aircraft Landing
Sep 2006 Alison Brown and Ben Mathews, NAVSYS Corporation

"...INTRODUCTION...
...The SRGPS [Ship Relative GPS] architecture provides a precision approach and landing system capability for shipboard operations equivalent to local differential GPS systems used ashore, such as the FAA's Local Area Augmentation System (LAAS). A relative navigation approach is used for SRGPS with the "reference station" installed on a ship moving through the water and pitching, rolling, and yawing around its center of motion. In addition, the ship's touchdown point may translate up/down (heave), side-to-side (sway), and fore and aft (surge). Since the shipboard landing environment is much more challenging than ashore, the SRGPS approach must use kinematic carrier phase tracking (KCPT) to achieve centimeter level positioning relative to the ship’s touchdown point...."

Source: http://www.navsys.com/Papers/06-09-002.pdf (0.5Mb)

Then for the first but NOT last time at: viewtopic.php?f=22&t=14115&p=204086&hilit=LAAS#p204086

JPALS: Not Just LAAS in Navy Uniform
01 Oct 2002 William Reynish

""The seagoing Joint Precision Approach and Landing System for the U.S. Navy provides much more than GPS differential accuracy corrections. It uses data link to give pilots a plethora of data from a host of sources....

...Extraordinary Environment
But the seagoing JPALS will be a horse (or a LAAS) of a different color. One of the biggest differences will be its data links. For, as development has evolved, carrier-based JPALS has become a generic term applied to a wider data link environment than just the automatic landing portion....

...since the carrier’s raison d’etre is to extend military air power in all weather, you could even say that the seagoing JPALS’ ultimate purpose is to thread the tip of an autolanding aircraft’s arrester hook through an imaginary 9-square foot (0.83-square meter) box centered precisely 14 feet (4.3 meters) above the pitching and rolling stern of a carrier in very low visibility, by day or night....

...At a 20-nm range from the carrier, the autoland level of data link operations kicks in. Uplinked data will include landing weather conditions, such as the all-important wind speed and direction over the carrier deck, plus the continuously updated GPS differential accuracy corrections similar to those required for a LAAS-like precision approach. The corrections will be similar but with much higher accuracy than those used in LAAS or the shore-based JPALS units.

Extreme Accuracy
To assure the exact positioning of the aircraft’s arrester hook within the very small area on the carrier deck, the Navy turned to the commercial survey industry’s real-time kinematic (RTK) GPS technique, which uses the carrier phase of the GPS signals to achieve accuracies within centimeters. The Navy requires horizontal and vertical accuracies of less than 15 cm (5.9 inches), with integrity assurance of no more than 1.1- meter (3.6-foot) error in 10 million landings.

Remember that imaginary 9-square foot box? The Navy has proved that accuracies of this type are possible in autolanding exercises with F/A-18s and other aircraft on carriers and land facilities, using a modified, prototype JPALS system in conjunction with RTK. The service also has demonstrated the system’s immunity to GPS jamming....

...But JPALS has the answer here, too. Real-time corrections for deck movement, derived from the carrier’s inertial navigation system, are continually uplinked to an aircraft, as it makes its final approach. The corrections are fed to the autoland system, which makes attitude adjustments all the way to touchdown–or, more precisely, to the point of placing the arrester hook exactly between the second and third arrester cables, four of which are stretched across the deck 40 feet (12.2 meters) apart. JPALS will bid farewell to the "bolter," that colorful expression used by naval aviators for an aircraft whose arrester hook misses the cables and is forced to make a missed approach. But in tomorrow’s Navy, bolters may simply be an undesirable impediment to 4D, high-speed traffic flows...."

Source: http://www.aviationtoday.com/print/av/i ... 12893.html

Somefing more ofisial? viewtopic.php?f=22&t=14115&p=256698&hilit=LAAS#p256698

A Hybrid Integrity Solution for Precision Landing and Guidance
April 2004 Kenn L. Gold and Alison K. Brown | NAVSYS Corporation

"Abstract
NAVSYS Corporation has designed a hybrid integrity monitoring solution for precision approach and landing in a GPS environment degraded by RF interference. The integrity solution described in this paper leverages the capabilities of next generation digital spatial processing and ultra-tightly-coupled (UTC) GPS/inertial integrated military User Equipment (UE). The design includes a spatial environment integrity monitor, a GPS/inertial RAIM solution that allows detection of small error drift rates before the blended solution can be corrupted and an integrity monitoring function embedded within the Kinematic Carrier Phase Tracking (KCPT) algorithms which provides a level of confidence on the final KCPT solution. Simulation results showing the expected performance of some aspects of this multi-level integrity monitoring approach are presented. A design for an aircraft GPS/inertial digital spatial processing receiver, the HAGR-A, is also included. This receiver, which is based on the NAVSYS Software GPS Receiver, will be used as a test bed for implementation and testing of these integrity monitoring techniques

Shipboard Relative GPS (SRGPS)
The Joint Precision Approach and Landing (JPALS) Shipboard Relative GPS Concept (SRGPS) is illustrated in Figure 1. The goal of the SRGPS program is to provide a GPS-based system capable of automatically landing an aircraft on a moving carrier under all sea and weather conditions considered feasible for shipboard landings. The presently utilized Aircraft Carrier Landing System (ACLS) is a radar-based system which was developed more than 30 years ago and has a number of limitations that make the system inadequate to meet present and future ship-based automatic landing system requirements. The goal of SRGPS is to monitor and control up to 100 aircraft simultaneously throughout a range of 200 nautical miles from the landing site. Integrity monitoring is especially important for the last 20 nm of an approach, and accuracy requirements are 30 cm 3-D 95% of the time.

The SRGPS architecture provides a precision approach and landing system capability for shipboard operations equivalent to local differential GPS systems used ashore, such as the FAA's Local Area Augmentation System (LAAS). A relative navigation approach is used for SRGPS with the "reference station" installed on a ship moving through the water and pitching, rolling, and yawing around its center of motion. In addition, the ship's touchdown point may translate up/down (heave), side to side (sway), and fore and aft (surge).

Since the shipboard landing environment is much more challenging than ashore, the SRGPS approach must use kinematic carrier phase tracking (KCPT) to achieve centimeter level positioning relative to the ship’s touchdown point. Faulty measurements, even if detected prior to transmission, impact system performance. Therefore, improvements are needed in the SRGPS shipboard reference station and signal processing to assure the continuity and integrity of the SRGPS corrections. Of particular concern are: (a) the robustness to signal blockages from the ship’s superstructure; (b) the ability to operate in the presence of multipath while maintaining the carrier-phase and pseudo-range integrity; and (c) the ability to continue operation in the presence of radio frequency (RF) interference (from both normal ship operations and jammers) in a tactical environment...."

Source: http://www.navsys.com/papers/04-04-001.pdf (0.35Mb) [no longer there if anyone interested I could probably find it to attach here?]

spazsinbad · by **spazsinbad** » 14 Apr 2019, 05:31

The ROBOT ONLY certified JPALS got it aboard on centerline as videos attest (could be just a repeat though). :devil:

X-47B ILARTS PLAT Carrier Approach Arrest View https://www.youtube.com/watch?v=Huhxyucp_AM

X-47B Program Update [seven CVN approaches via Nose Wheel Camera] https://www.youtube.com/watch?v=V0b384xslgI

7 X-47B CVN Carrier Approach Touchdowns Nose Camera View https://www.youtube.com/watch?v=qgkoTu4JS-Y