|Demise of the Flight Navigator|
|Mike Grierson FN 5416 (Nov 1974)|
Master Air Navigator 845
The Flight Navigator, like the professional Radio Operator, has long been forgotten in civil aviation. Despite this, there remains a provision in law for the Flight Navigator; and there remain 2 licensed Flight Navigators holding CAA licences.
Article 25 of the ANO (2005) states that:
(9) An aircraft registered in the United Kingdom engaged on a flight for the purpose of public transport shall carry:
(a) a flight navigator as a member of the flight crew; or
(b) navigational equipment suitable for the route to be flown;
if on the route or any diversion therefrom, being a route or diversion planned before take-off, the aircraft is intended to be more than 500 nautical miles from the point of take-off measured along the route to be flown, and to pass over part of an area specified in Schedule 7.
(10) A flight navigator carried in compliance with paragraph (9) shall be carried in addition to any person who is carried in accordance with this article to perform other duties.
Schedule 7 lists the following areas where there are by and large few if any ground based navigation aids:
|A Arctic||G Indian Ocean|
|B Antarctic||H North Atlantic|
|C Sahara||I South Atlantic|
|D South America||J Northern Canada|
|E Pacific Ocean||K Northern Asia|
|F Australia||L Southern Asia|
The term Navigator has its origins at sea where the art of travelling long distances without any significant landmarks has been developed over the centuries. Basic techniques changed little over the years until the advent of the aeroplane with its ability to cover large distances in a relatively short time. Initially called observers, the military navigators did not become formally recognised as such, until the Second World War. Airborne navigation was developed to facilitate the movement of aircraft around the World and more specifically, to pinpoint targets for bombing. Many of the techniques were based upon traditional maritime practice, whilst the need to deliver bombs accurately to their targets, resulted in the development of radio navigation aids and sophisticated mechanical navigation computers.
The Royal Air Force has continued to train navigators to the present day however, they have been renamed Weapons Integrated System Officers or Operators known as either WISOs or WISOPS, or maybe just WIZARDS!
To the many aspiring airline pilots the ATPL theoretical examinations appear somewhat daunting, and certainly encompass many aspects of aviation that future pilots are unlikely to ever have to put into practice. The navigation subjects can be traced directly back to the RAF Navigator training of the 1940s and 50s. Prior to the formation of the Civil Aviation Authority in 1974, the RAF College of Air Warfare then located at Manby in Lincolnshire, vetted all navigation question papers set for civil airline pilots and navigators.
To many, the role of the navigator is not clearly understood; I recall a flying scholarship student asking the question “what exactly do navigators do?” Following the explanation, he paused for a moment and then said, “so what do the pilots do then?” The answer of course was, they do as they are told, and if they are lucky they may get to do the landing as well.
The role of the civil Flight Navigator was somewhat different to that of the military counterpart. Many civil flight navigators originated in the merchant navy, where they had developed the skills of ocean crossing using the marine sextant once a day. The pilots would operate the aircraft to the coast using ground based navigation aids, ADF, Radio Range and later VOR, and once outside the range of the ground based aids, the navigation was handed over to the flight navigator who would then fix the aircraft's position using very little equipment other than a sextant. The principal method of navigation was dead reckoning using Air Plot. This technique involves plotting heading and airspeed as vectors on the chart; fixes are then taken using a sextant at regular intervals. The vector difference between the air position and the fix, represented the average wind for the period since the last fix; this could then be used to aid further dead reckoning ahead of the aircraft. The requirement to use astronomical (Astro) navigation techniques dictated that over water flights should be conducted at night in order to give the best opportunity for fixing, during the day there is only the Sun, whereas by night the stars are visible if the aircraft is not shrouded in cloud! Once the aircraft reached the coastal fix, the navigator was largely redundant for the remainder of the flight.
In contrast, the military navigator was involved in the entire mission, providing guidance to the pilots with the probable aim of arriving at a target using a minimum of active navigation equipment that would identify the presence of the aircraft.
The V-bomber force practiced precise navigation exercises involving flights of up to 2000 miles with all transmitting equipment turned off. Two navigators (Plotter and Radar) would determine the position using astronomical sandwich fixing, a very precise but labour intensive technique requiring the radar navigator to have his eye glued to the sextant for up to 15 minutes in every half hour. Once within range of the target, the radar navigator would then operate a ground mapping radar in short bursts to identify ground objects from the jumble of radar returns, to update the aircraft position more precisely. The popular paperback Vulcan 607 www.britains-smallwars.com/swbooks/Vulcan-607.html gives a fascinating insight to how the crews operated. The radar provided slant range information, which had to be computed into plan range, using a sophisticated mechanical computer containing a mechanical triangle solver. The precise height of the aircraft over the ground was also required for bombing, so the altimeter had to be calibrated using a series of height finding techniques, and corrections applied using another mechanical computer. The early gyro magnetic compass systems employed a crude DC transmission system between the many compass repeaters; errors comprising any multiple of 3 degrees were possible, necessitating constant compass comparisons. As these systems were replaced with more sophisticated synchronous compass systems, this process of compass comparison continued ad infinitum.
The Navigation Position in the Vulcan MKII Bomber
Pictures courtesy of Vulcan Preservation Society—Wellesbourne Mountford
The navigation equipment used in the three V-Bombers, Valiant, Victor and Vulcan was basically the same. The MkII Victor and Vulcan aircraft were however fitted with updated versions. Many interesting names were used to describe equipment; Blue Silk and Green Satin were code names for the Doppler radars, whilst H2S (derived from Home Sweet Home) was the name given to the ground mapping radar originally devised for the Lancaster. Mk1 V-Bombers were fitted with a hyperbolic navigation aid codenamed GEE, another WWII development, which provided information that then had to be plotted on a special chart to give the aircrafts position in Latitude and Longitude. The V-Bombers were fitted with a number of computers, all analogue; electro-mechanical devices and masterpieces of precision engineering. The navigation-bombing computer had its origins in the Hotpoint washing machine factory in Peterborough. Inside the computers were some very clever devices, Sine potentiometers (pots), Cosine pots and double Sine/Cos pots, even a Square Rooting Pinwheel; the name Widget is believed to have been given to some unknown part of a mechanical computer; alas, it has now been relegated to the bottom of a beer can!
The military transport navigator fulfilled a similar role to the civil flight navigator, except that there was more involvement in the overland legs. The navigator on a transatlantic flight would probably start planning some 3 hours or more prior to take off. The route had to be determined, and would be based upon the minimum flight time. This involved a process of selecting a route based upon the forecast met chart, avoiding headwinds when westbound and looking for the jet stream when eastbound. Quite often, westbound routes would appear inordinately long, yet the flight time would represent the shortest possible. Navigators were responsible for fuel planning and on strategic transport aircraft also completed the take-off performance planning as well. Navigation equipment was usually based upon a Doppler radar providing drift and groundspeed, hopefully this would drive a Ground Position Indicator (GPI), which represented a major advance from the earlier Air Position Indicator (API) or the drift sight fitted to earlier transport aircraft. Radio aids could include LORAN A and or LORAN C, both of which required considerable operator skill and experience. These were long range versions of the earlier GEE system, and survived until relatively recently. These low frequency aids, required a relatively large antenna system making them very inefficient in jet aircraft. Position fixes were compared with astronomical observations, whilst the compasses were checked for accuracy against the azimuth of a celestial body. It was not uncommon in mid Atlantic to have a position error of 25–30 miles. Consequently, the track spacing used for oceanic crossing was commensurately large.
The Navigation Position
The increase in North Atlantic air traffic throughout the 1970s brought about a number of changes, the wide track spacing (120 nm) had to be reduced, necessitating a greater navigational accuracy. Minimum Navigation Performance Specification (MNPS) airspace was borne in the North Atlantic area necessitating a change in operating procedures. Aircraft unable to comply were denied access to airspace above FL 290 with a consequent fuel penalty. Advances in long-range navigation equipment resulted in the introduction of Omega and Inertial Navigation Systems as standard fit in the modern jet aircraft, eliminating the need for a separate navigator. Older aircraft were often not retrofitted and retained flight navigators for a further 10 years. The military aircraft were seldom retrofitted as this invariably cost more than the navigator. In the 1960s, the mighty Hercules with its superb navigation fit was probably the only aircraft that knew exactly where it was in mid Atlantic, yet by the 1980s using the same equipment it became the only aircraft that did not know where it was, simply because everyone else had become more accurate. Military jet aircraft could not endure the fuel penalty of being excluded from MNPS airspace and so adopted a sit on the fence approach. Aircraft such as the VC10 were re-equipped with Omega and a single Inertial Navigator (Ex BOAC VC10s), but a third box needed to check the accuracy of the other two, was never fitted, there was no filtering of navigation information other than the Navigator operating in the time honoured manner checking sophisticated equipment against astronomical observations.
Navigation Position VC10 C Mk1
(Retrofitted with Inertial Navigation
System and Omega)
The navigator carried topographical charts to cover the entire route to be flown. On a round the World flight this usually required a second Nav Bag packed full of 1 million scale maps; on the jets, the bulk was reduced by using 2 Million scale maps. The accuracy of the inertial navigation units was relatively good; however, the position could degrade by up to two miles per hour plus an additional 2 miles. After a ten-hour flight this could lead to a typical error of 22 miles. Errors were invariably greater on eastbound flights where the aircraft was travelling against the earth’s rotation. Even the most sophisticated radio navigation equipment proved to have areas where its accuracy was far from desirable, giving rise to names like the Winnipeg hole, an area of Canada where Omega signals disappeared with monotonous regularity. Navigation in Polar Regions required specialised techniques including Gyro Steering. This could require alignment of the gyros with a datum that differed considerably from True North or magnetic North and frequently confused the pilots. Homing to a VOR aligned to Grid North with a relative bearing at 90 degrees to the aircraft heading, leaves the mind wondering. Even today, GPS is not aligned to give good satellite geometry in Polar Regions with a consequent loss of accuracy. The mechanical GPIs used a ball resolver to determine longitude as a secant function of the local latitude. This device was prone to slippage (akin to driving a car in ever decreasing circles on a slippery surface) if used at high latitudes (70 degrees or more), making the device inaccurate, consequently, it became standard practice in RAF transport aircraft to navigate using a grid overlay on the chart and operate the GPI using a false latitude close to the equator where the device was most accurate. Variation and Convergence then combined algebraically to give Grivation, headings were Grid, not True or Magnetic. The art of navigation is becoming lost; some of the remaining navigators now use their skills to teach navigation to potential airline pilots in our ground training schools but sadly, these future pilots are unlikely to ever have the opportunity to practice the art, as the aeroplane can now do it better by itself.
New generation aircraft with glass cockpits have totally eliminated the requirement for specialist navigators. Civil operators probably ceased to use navigators by 1980. The RAF continue to use navigators on many of its ageing aircraft however, the replacement aircraft scheduled to come into service over the next few years will no longer carry a Navigator, the Nimrod replacement will remain the final bastion of the Navigator or WISO as they are now called. The two remaining civil UK Flight Navigators are very much the last of an era.
One of the last two remaining
CAA Flight Navigator Licences
When I was a little boy, my parents threatened to send me to Timbuktu if I misbehaved; One day I made it: