VFR to IFR - Flying in Clouds Required Flight Control Instruments and Radio Aids. Gyro technology available earlier but had to reach cockpit.
Copyright 2011 Franklyn E. Dailey Jr.
Triumph of Instrument Flight
A Foreword: This is one of two introduction pages for those who might
be interested in the author's book on aviation, pictured at left. Early draft
material for that book can be found in links down the lefthand column relating
to chapters in the book. There is a second introductory page
Lindbergh-1931Sirius, Doolittle-1929 flight, Amelia
Earhart-1937, Pearl Harbor 1941, Stinson SR-10, Convair P2Y-1,that contains
information that we have been able to add after the book was published in
2004. That page contains "errors and amplification" for the book, in addition
to other pilot experiences. One of these, republished with author Robert
Mudge's permission, came from his very important aviation book now out of
A career that attracted many World War I aviators, and young enthusiasts who had learned flying from them, was a career flying for an airline. Airlines were in their formative years in the United States in the late 20s and early 30s. The opportunity to be involved in building a new enterprise was not lost on men who became excited that their newfound flying endeavor, which they loved, could also offer a workplace career.
The airlines that formed and grew in the 1930s were creating a story of transition from bare beginnings to early maturity. The aircraft they flew and the engines that powered them, the route structures they pioneered, and the schedules and markets they established formed the foundation for the air transport business we know today. For this story, the developments in instrumentation, communications, pilot proficiency and ground support all took form in this amazing decade. The ability to conduct flight safely in weather was the mark of success.
Some railroads took their passengers for granted while others linked up with new air transport companies. A new generation of field salesmen wanted to go eyeball to eyeball with customers who were too many railroad-days away. What would become major U.S. trunk airlines took form in the late twenties. These began as very small enterprises. The route structures were limited compared with a latent demand that led to the high density of air connections later on. In the early years air transport expansion was done with the zeal of pioneers who surprised themselves and their early passengers with the pace of commercial aviation progress. Though the transport aircraft available at the outset had limited cruising ranges, the competitive modes of transportation were filled with the impediments of land, and what man had contrived to put on that land. The air had no such impediments. Investors, pilots, attractive routes, and reliable aircraft came together in the first order of business. Competing with scheduled land transportation required reliable flight schedules. That was the first order of business and it was a big challenge. The air transport business was a new business. Building aircraft was a new business. Powerplant development was a new business. All proceeded almost independently with each of those enterprises pursuing goals that seemed generally valid but this occurred well before the airline executive routinely defined what airframe and engine would best suit his business. The business developed in the direction that available equipment would support.
Other groups of visionaries saw that airports, radio aids to air navigation and a communication and control infrastructure would be needed. The powerful rotating light beacons used in the very early days to help early mail pilots find their way from point to point across the United States did not penetrate very far into the clouds.
Despite the acknowledged risk of flying, pilots were eager to sign on to the new challenge of scheduled flight with paying passengers. Those pilots found partners willing to share those risks in marriage. The family man, a breed of pilot different from the record setters, needed a regular salary. Along with risk-taking investors, these aviators collaborated in the birth of an entirely new business opportunity, which came to be known as an airline.
These early passenger carrying aviators also proved, to themselves initially, that Contact Flight Rules, CFR, the rules for proceeding from one point to another by means of visual sighting of recognized earth landmarks below, were not going to be sufficient to build an air transport industry. Acronyms such as, CFR for Contact Flight Rules and VFR for Visual Flight Rules were coined. Often these terms were used interchangeably.
In the course of this one critical decade, the 1930s, a growing number of passenger flights began to have an impact on early flying rules that often were borrowed from rules of the sea such as the seaman's General Prudential Rule. Powered aircraft gave way to powered blimps and zeppelins. Those in turn gave way to un-powered gliders and these in turn gave way to manned balloons.
"General aviation" dominated early flying with its pilots who took off, flew locally and landed at the same airport. These men had passed tests promulgated by the U.S. Civil Aeronautics Authority. They learned to fly observing Contact Flight Rules, CFR. Gradually,VFR, for Visual Flight Rules superseded CFR as the operable term. "Contact" had derived from maintaining contact with the ground. "Visual" incorporated that ground contact responsibility but added the responsibility to maintain visual contact with other aircraft in the air space. The subtle differences were a challenge even for those in the profession to distinguish. I am not going to try here. For pilots and for the flying public, what the human eye can "see" from the cockpit has not diminished in importance.
Instrument flight, conducted under IFR-Instrument Flight Rule conditions, meant that a plane and its pilot did not have to descend every time clouds were encountered in the sky. Many factors contribute to instrument flight capability. Among the factors are pilot proficiency, communications, ground and aircraft instrumentation that became increasingly electronic-based, and airport design, especially with runways of sufficient width, length, adequate lighting and good approaches.
By the early 1930s, proficient, safety-minded airline pilots together with increased aircraft systems reliability, were demonstrating that aviation as a commercial enterprise was here to stay. At the end of the decade, safe instrument flight had become an almost routine practice.
With the onset of World War II in Europe in 1939, progress in instrument flying had become the "third rail" for U.S. civil aviation along with safe airframes and reliable engines. The advances made in U.S. commercial aviation in the decade of the 1930s benefited the future military pilots of World War II in many ways. The flight proficiency standards for military pilots improved as the experience gained in civil aviation was passed along. Many commercial airline pilots were also reserve military aviators.
Along with the introduction of radio aids to air navigation, the thirties saw air traffic control systems installed across the United States. The nations civil airways system was created. The impetus for the establishment of air traffic control systems was the safe conduct of aircraft in instrument flight conditions. By World War II, these airways had begun to crisscross the United States. It would be accurate to note in 2002, that if the United States atmosphere were perfectly clear of all clouds and smog every day, the sheer volume of commercial flights would demand an air traffic control system comparable to or even better than the system we actually have now.
Many young World War II military pilots were thankful that at least over the early legs of their deployment to their advance operating bases, a domestic airways system was in place. Those military pilots in turn helped establish airway and traffic control systems extending over the northern rims of the Atlantic and Pacific Oceans. Success in flying the north Atlantic was vital to victory in Europe in World War II. Success in flying the north Pacific helped blunt any intention that Japan might have had in expanding their early Aleutian success. After World War II, both the north Atlantic and the north Pacific became areas in which tests of our resolve in the Cold War were met. And for the airline transport business, these northern routes were essential.
The advance in the art of instrument flying moved forward with the advances in weather forecasting, weather reporting and the development of commercial aircraft capable of comfortable flight at intermediate altitudes. Early transport aircraft were not pressurized or were pressurized to fly only at relatively low altitudes. Cumulus cloud buildups (thunderheads) can rise above 50,000 feet. Detouring around the upper reaches of those buildups enabled a safer, less turbulent flight for the later jet-powered, pressurized, commercial aircraft. Earlier aircraft had no choice. If they were to proceed, they had to penetrate this weather and the choice of altitude to penetrate was often the critical decision. In air traffic control's first years, controllers did not have sufficient flexibility with their technology to send aircraft off the low frequency defined airways system to make wide sweeps around weather. Microwave radar eventually provided the tools to make such procedures possible.
Weather forecasting and increased flexibility in the radio range route structure combined to aid in weather avoidance. It became possible to vector air traffic around the worst of weather's in-flight hazards even before the advent of modern jet powered, pressurized aircraft, moved commercial flights into the upper reaches above 35,000 feet and above most weather. As weather reporting for flight purposes developed into regular broadcasts, an airfield's "ceiling and visibility" broadcasts found the pilot's ear especially receptive. Even with advances in instrumentation, CAVU, for Ceiling and Visibility Unlimited, was always a welcome condition.
The many ways in which variations in visibility can influence a pilot's judgment are important to the story of instrument flying. The most welcome visibility condition, and the one in which aviation was first practiced, was daytime, without fog or rain, and before smog began to obscure major population areas. A second condition occurs in morning or evening twilight where visibility can be hampered by something as innocent as a blinding sun. The third broad condition of visibility occurs in night hours, again in clear weather. Darkness is an impediment to an immediate grasp of a visual horizon. Night flight under good visibility conditions is more of a challenge to the inexperienced pilot than flight in daylight. Night flight over areas with ground haze can lead to disorientation if the pilot fails to keep a respectful grasp of what his instruments are telling him or her. The stars above, in a cloudless sky, help establish a visual reference. A descent into haze loses that night horizon reference and adds the challenge of lowered forward visibility. There still may be lights on the ground below to help give the pilot sufficient reference. If the descent is into haze over water, there are no ground lights, and visual reference above and below can be lost. Instrument flight is the only recourse. Attempting to shift to instrument reference may come too late and the pilot can become anxious, distrustful of all information, and then completely disoriented.
Instrument conditions introduce a broad spectrum of flight situations. Generally, for level flight at altitude on instruments, the condition of darkness does not add much to the challenge for the experienced pilot. In an approach to landing on instruments, the changeover phase in which the pilot makes initial visual contact with the ground can present a different challenge in darkness as compared with daylight. Among the factors are; the pilot's forward visibility at the field; whether clouds present a well defined or a ragged ceiling; the horizontal and vertical geometry of the instrument approach patterns; the profusion of structures and their lighting in areas immediately adjacent to the airfield. All play a part in determining whether day or night presents the simpler condition for pilot judgment.
An airline once provided even its most experienced pilots a familiarization trip over a route before assigning the pilot to a route that he or she had not flown before. The "fam" flight has all but disappeared according to recently retired Delta airline Captain Robert E. Mitchell. It is still in practice for the first flight across an ocean. For a time, special airports led to a pilot requirement to examine 35mm slides of its terrain and approaches, but that is no longer required. Mitchell, who flew for Delta for 31 years, and the Navy before that, stated that after an initial qualification in an aircraft, the so-called "mother-in-law ride," no further familiarization flights are assigned.
The "ceiling" at a United States' airfield is a number in hundreds or thousands of feet that defines the base of the cloud cover. Much of the time this ceiling, or base of the lower clouds, is quite uniform and the number that is broadcast is conservative, that is, the lowest ceiling is defined rather than any attempt to present an "average" base of the clouds. At one time, a balloon would be released from a ground station. Knowing its rate of ascent, the ground station could calculate the ceiling when the balloon disappeared in the clouds. In later times, automatic and continuous measurement of ceiling, by means of optical ceilometers, has nearly eliminated the use of balloons.
There are times when an aircraft proceeds in and out of clouds that it experiences a "ragged" ceiling. This occurs too when the aircraft is flying in an out of the "tops" of the clouds. The practical impediment is a visibility condition. When the aircraft is in clouds, whether in a solid overcast with a well defined ceiling below or in a ragged overcast in and out of clouds, the operative forward visibility should be considered to be zero. Passengers or non-flight personnel may be able to intermittently see the ground below but that information is not useful for a pilot flying a conservative flight pattern in instrument conditions while approaching a landing field.
Lighting has played an important role in air transport progress. In the 1920s, night pathways of light beacons were constructed across the United States. These rotated much like a lighthouse for mariners. A pilot making a flight at night under visual flight rules could derive navigation information from these lights. Maps were available to give the airman a defined location for each beacon. An understanding of the beacon characteristics could help a pilot determine whether he was proceeding on his intended course.
For landing at a field, the approach end of a runway has long been marked by four required green lights in a line directly across the runway. Almost flush to the ground, along both sides of the long axis of a runway, a series of white lights defined the "runway in use" at an airport. In the early days, these were called CAA, for Civil Aeronautics Authority, lights. These lights were early requirements for airports serving commercial passengers. Private airports of any size would also attempt to configure these standard lights. Operators flying passengers on a chartered (non-scheduled) flight could often hope to encounter field lighting consistent with the larger fields.
Later, some airfields, particularly those anticipating regular use for instrumented landings and takeoffs, installed additional lights called Bartow lights. These were much brighter than CAA lights, and their intensity could be controlled through five levels. The fact that a pilot could ask for, and almost immediately receive, a change of intensity, helped focus the pilot's eyes on the outlines of the landing surface. Bartow lights in the 1940s were not flush with the ground. In a marginal situation, for an aircraft that no longer had an option to reach a suitable alternate landing field, the risk of knocking off a few light stands was considered acceptable in the tradeoff for a successful emergency landing. As instrument flying developed, certain runways at an airfield were designated as "instrument" runways. For these runways, lighted extensions in both directions came along a bit later to give the pilot confidence that he was on the correct path before he reached the approach end of his runway