David Wall, a Sea King pilot from the mid-1960's era, indicates
the Sea king was only fitted with the following electronics:
UHF radio, one HF radio, IFF, ADF, Tacan, Doppler and a Radio Altimeter
plus a Dipping Sonar.
Ian Snow who did three tours as a TACCO (Air Navigator) on the Sea King
offers some insight into the Sea King's electronics suite during the time
he served.
"I first went to the Sea King in the Spring of 1973 joining HS-50 Squadron
which split into HS 423 and HS 443 Squadrons about 18 months later.
From 1976-79 I served in 443 Squadron and again in 1985-86. For communications,
the helicopter was fitted with the AN/ARC-552 UHF set, the ARC-505 (Collins
618T) HF transceiver and the Collins CU-351 Antenna tuner. The HF
antenna was the standard USN Sea King fit. It came out of the hull on the
port side just aft and above the passenger window, went forward to a short
mast on top of the port sponson, then back to the tail boom. The
Shearwater Base frequency was something like 5718 KHz but the antenna wasn't
very efficient at that frequency.
On the 20 metre amateur band it did however work well. Amateur
radio operator Brit Fader VE1FQ [1] , used to do the odd phone patch
for me if we were far enough from the ships. We were almost always
under imposed HF radio silence. The call sign exchange was "Brit
are you there?" followed by a "Standby" and a phone ringing.
HF COMM
The upper limit was 20 MHz for the Sea King using the CU-351 antenna
tuner.
VHF AERO COMM
The Sea King didn't receive aeronautical VHF until 443 Sqn went to Patricia
Bay in British Columbia. Since this was a civilian airfield, it didn't
have military UHF (225 to 399 MHz) capability.
As part of the CH-124A upgrade circa mid-70's, the Sea Kings were fitted
with a Wolfsburg commercial VHF FM set. The radio box was the same
but that there were several control heads that could be used depending
on the role. We had an 8-channel model but you had to pull the control
head out of the console in order to program the thing. The reason
we had it was for marine SAR, usually monitoring channel 16.
We had the trusty AN/ARC-552 when I first went onto the Sea King.
They upgraded it but I don't recall what the new model was. They
also upgraded the TACAN. There was an electronics compartment
under the pilot's feet and slightly forward. Access was through a
huge door that formed the bow. All that the tube gear was replaced
by radio equipment that went into the floor console between the pilots.
Eventually "lead pigs" had to be installed up front to keep the center-of
gravity in bounds.
The Nestor Secure Voice system was a total disaster. We discovered
after awhile that the problem was mostly with the narrow bandwidth of the
ARC-552 radio. Basically if you couldn't see the other aircraft you couldn't
talk to it. The upgrade to Vinson Secure Voice and the upgrade to
modern radios eventually fixed the situation.
In order to locate submarines, the Sea King's latest sonar uses a transducer
ball at the end of a 450 foot cable. It can also be fitted with FLIR (Forward
Looking Infra-Red) to find surface vessels in the dark of night".
DIPPING THE SONAR and PROBLEMS WITH THE RADAR ALTIMETER
In the Sea King, in order to dip the sonar dome, the pilot would establish
forward flight at 150 feet altitude and 100 kts into the wind based on
the barometric altimeter and on the TACCO's "mark dip" command would punch
the "coupler" button. The coupler would then bring the helicopter
down to a hover at 40 feet ASL based on the radar altimeter reading.
As the Doppler radar was transitioning from forward flight mode into hover
mode (+/- about 10 kts) the pilot would order the sonar dome down and the
ball would go into the water at about the time zero speed was reached .
Zero was relative to the earth's surface since the helicopter is really
flying forward at the speed of the wind. The Doppler radar is manually
compensated for the direction and speed of the moving sea - swell and/or
waves, none of which are necessarily going in the same direction let alone
the wind.
Once the ball reached 50 feet (depth) the coupler would switch from
using the Doppler radar as the reference to two angle sensors incorporated
in the reeling machine and the coupler would 'fly' the helicopter
to maintain position vertically over the sonar cable. In theory,
if the radar altimeter failed the coupler would cause the helicopter to
climb back up to 150 feet.
One of the Sea King's modifications was triggered by a failure of the
radar altimeter while dipping the sonar transducer. The problem was
that it didn't quite fail (in which case the flight stabilization system
would revert to the higher barometric altimeter setting); rather, it started
to send bogus data which resulted in the hover control system lowering
the helicopter rather than raising it above water. The radar altimeter
emitted a CW transmission that swept from 4200 to 4400 MHz. There
was a coax timing delay line between the transmitter and receiver.
The calculated difference between the outgoing and incoming frequencies
translated into distance above ground or sea surface. There were
three or four instances of the helicopter very gradually descending (with
the first instance at night) over a pretty calm sea in fine weather.
On the first instance, the co-pilot leaned over and turned on the windshield
wiper to clear "rain" from the windscreen. A moment later the pilot,
realizing that it was spray generated by the rotor wash, executed an "Emergency
Streamer" - a controlled climb of several hundred feet until the sonar
ball broke the water, followed by a transition into forward flight and
recovery of the sonar cable/dome. On the second occurrence of the
problem, the waves were touching the tail wheel causing the helicopter
to pitch. That was followed by a couple of daytime instances when
the crew was able to maintain a manual (visual) dip and assess what was
really going on. The situation resulted in an operational restriction
on night dipping that lasted for 3 years until a fix was developed for
the radio altimeter.
A temporary fix to the problem was to equip the helicopters with active
sonobuoys and sonobuoy receivers taken from the retired Argus a/s aircraft.
This system was not supplied with chart recorders, just chronometers to
measure the time between the active "ping" and the received echo.
It was very elementary indeed. The ideal system would have been a proper
passive acoustic system like the ASQ-13C dipping sonar which had a passive
acoustic processor incorporated in it.
USING THE AN/APS-501 RADAR
Getting radar into the Sea King revolutionized operations. Until then,
the ship had radar-controlled the helicopter much as if they were
on the end of a string. Although the APS-501 was not the best antisubmarine
radar, it could at least find Mother (the ship) who refused to turn on
Father (the TACAN). It allowed the crew to do their own radar, self-controlled
landing approach. Because of the radar blind spot produced by the
rotor transmission, the pilot would bring the ship down the upwind side
of the blind arc and a good TACCO (Tactical Coordinator, code word PLAYBOY)
could bring the pilots into a 175-200 yard proximity of the ship's hangar.
It took lots of practice but the technique prevented a ditching at
sea on a foggy night.
NAVIGATION INSTRUMENTS
The outputs from the navigation equipment would be fed to some form
of amplifier which would send the information to the display instrument.
Some aircraft would have only magnetic orientated instruments, other (naval/maritime)
aircraft would have a true north display capability.
For example, in the Sea King the BDHI (Bearing Distance Heading Indicator)
had a rotating compass card that could be selected to True North, Magnetic
North or Track. In tactical mode, the pilots would select Track since
the TACCO was giving them a true bearing (#1 needle) and distance to go
to the "Mark Gate" point for the next dip. The pilot was actually
flying some variant of an 'S' type pattern since he had to go into and
out of the dip heading into wind (the sub of course would try to escape
down-wind to minimize the amount of time that contact could be maintained.
When flying an approach to an airport the pilots would select "Mag" since
all civil air operations use magnetic headings.
Speaking of navigation, there is an old tale where the controller orders
a 1° turn to the right. When the pilot replies that nobody can fly
that accurately, the controller says “OK turn left 9°” followed
by “Turn right 10°”.
AN/ASN-501
David Wall, a former Sea King pilot, provides some background on the
ASN-501. "It was a tactical navigation plotter and was first installed
in the Tracker. When I was at Shearwater, it was still at VX-10 Squadron
with the first units just making their way into the aircraft at VS-880.
Prior to that, the navigation and plotting of sonobuoys was done by the
co-pilot using a Mk VI plotboard on his knees, his control column having
been stowed away out of sight.
The ASN-501 was a great improvement over the "board". It had a mechanically
driven plotting screen about a foot square and centrally mounted between
the pilots on the front instrument panel. It was very crude by modern digital
standards but a great advance in those days. I left Shearwater in 1966
and sometime fairly soon thereafter, the 501 found its way into the Sea
King but for a variety of reasons it was placed in the back and operated
by the crew stationed there. I think there were several reasons for this
decision – lack of space up front, a requirement for both pilots in the
Sea King to be in the “flying loop” especially low level at night, availability
of a crew in the back The only sensor back there at that time was the sonar
and that just took one man to operate. Probably the real reason was that
integration/unification of the Canadian Forces was underway with the Airforce
taking over what had been naval aviation, and the Airforce had tons of
navigators looking for work.
None of the above is to be confused with TACAN, which is simply a navigation
system that feeds bearing and distance information to round dial readouts
on the instrument panel for the pilots. It was a naval system developed
by the USN in the ‘50s and was a UHF equivalent to the civilian VHF VOR
navigation system with the added feature of DME displaying distance (that
VOR could not). In the ‘60s, most airways were VOR based and the TACAN
stations were strictly military which made for some interesting cross-country
flying since our RCN aircraft were TACAN (and ADF) only. Gradually, the
civies realized the value of the DME readout so TACAN beacons were co-located
with the VOR stations creating the now familiar VORTAC designator. TACAN
frequencies were hidden to the pilot, who just dialed in a channel number,
whereas the VOR stations were selected by the frequency – eg. YOW 114.6
paired with Channel 93. Civilian aircraft simply added DME receivers which
paired up with the appropriate frequency when a VOR station was selected".
AN/ASN-123
The Teledyne Systems AS/ASN-123 was initially developed for the US SH-2F
helicopters and then adopted for service in the SH-3H Sea King and the
EA-6B Prowler. The set is a Tactical Navigation System but in helicopters
it also provides the torpedo attack solution. In a helicopter, the main
system display is in the cockpit but the TACCO has and operates the main
system control panel.
The six Sea Kings (five deployed, one reserve) converted to the
anti-surface role for Gulf War 1 received the ASN-123 as part of the conversion.
The remaining helos would have been converted sometime later when the life
extension program was commenced.
PLOTBOARD
Calypso was an advanced acoustic processor (passive and active)
in the HOTEF (Helicopter Operational Test and Evaluation Flight) lab at
Shearwater, NS . It was being evaluated as a candidate for a Sea
King upgrade in support of the CANTASS tactical towed-array on Halifax
class frigates. The flying version went down with the HOTEF Sea King when
it suffered a main transmission oil leak, ditched, and eventually
sank. It was flying from HMCS Fraser, the CANTASS towed-array trials
ship.
SERVICE LIFE COMING TO AN END
Major Dwight Bazinet, known in Shearwater as "Baz", comments on
the Sea King's electronics fit to the extent that he can. He is currently
on his fifth posting to HOTEF and as of June 2015, is the Augmented Surface
Plot (ASP) functional tech lead and lead software developer. For the Sea
King, he indicates:
- the FLIR-2000 has been retired
- the ASN-123 has just been completely removed.
- the basic ASP is fitted in the TACCO position of all the aircraft.
ASP is a system that optimizes the tactical plot
by overlaying maps, radar, AIS, and tactical graphics. A detained
article on ASP from Canadian Naval Review
Vol 9, No 1 (2013) can be viewed
here.
- All Sea King B models have ARC-210 radios.
- Installed is TCDL (Tactical Common DataLink). It is a mission kit
which employs a high bandwidth radio that can move various information,
including plot and video, to and from the ship; the actual box is a L-3
Comms Systems West CMDL).
The main thing we are doing with the Sea King now is using it to learn
how to use the CH-148 Cyclone.
FOOTNOTES
