Flying aircraft under IFR and VFR

Instrument flight rules (IFR) and visual flight rules (VFR) are the two sets of regulations governing civil aviation aircraft operations. In general terms, pilots decide to fly a VFR flight or an IFR flight (if they are suitably qualified) depending on a range of factors, including cloud ceiling, visibility, the kind of airspace, time of day and which country they are operating in.

Under VFR you can see where you are going – you can see the horizon across a broad and expansive area. You can judge the flight of the aircraft from visual references

Looking at VFR

Under VFR, an aircraft is flown ‘by eye’ with visual reference to the horizon, buildings or terrain to maintain ‘separation’, i.e. a safe distance from obstacles. This separation is often set to a specific figure dependant on altitude for IFR aircraft, whereas VFR craft maintain a ‘see and avoid’ principal outside controlled airspace. When the visual meteorological conditions (VMC) are favourable, VFR is the usual way to fly a small craft. Under VRF, however, a pilot cannot fly through clouds, which means they must go under, around or divert if the clouds form a vertical column and block the route. In some countries, such as Germany for example, under VFR you can have visibility of just 1.5 km, but you must also be able to see the ground. Night flying rules vary according to country – Germany allows VFR by night but Spain does not.1

Alex Stobo, director of operations at Bond Air Services, Babcock Mission Critical Services Onshore in the UK, explains: “Under VFR you can see where you are going – you can see the horizon across a broad and expansive area. You can judge the flight of the aircraft from visual references.”

Under VFR, a pilot will usually take advantage of flight instruments too, as Mike Biasatti, a single pilot IFR HEMS flyer and founder of EMS Flight Crew who is based in San Antonio, Texas, explains: “Flights undertaken with VFR conditions prevailing use GPS navigation for a straight-line point-to-point trip. Part of any flight is a good cross-check of your instruments, altimeter, airspeed etc., as well as monitoring gauges for each engine, transmission and hydraulics. So, while under VFR your primary focus is outside, you need to stay on top of anything happening outside the expected.”

Flying under IFR

On the other hand, flying under IFR means relying on aircraft instruments. According to the US Federal Aviation Administration (FAA) Instrument Flying Handbook, an IFR flight ‘depends upon flying by reference to instruments in the flight deck’, and ‘navigation is accomplished by reference to electronic signals’. IFR is generally used when visual references outside the aircraft are obscured by clouds, rain, fog, darkness or dust and flying via VFR is deemed unsafe. IFR allows an aircraft to fly in instrument meteorological conditions (IMC) and must always be used when flying in Class A airspace – commercial aircraft worldwide must always operate under IFR.

Stobo explains that UK HEMS missions are preferentially flown under VFR if possible, but must be IFR in controlled airspace. “There’s the possibility that a pilot would lift from his base, fly an approach to an airport on the runway, break off the approach and then fly visually to the HEMS site. That is one example when they might launch IFR, but ultimately the landing has to be done under VFR.” 

Whether a HEMS pilot will fly under IFR or VFR is also down to prevailing weather conditions. Biasatti flies for a programme in the US whose IFR capability means that the crew often accept flights that have been turned down by VFR bases/operators. “Forecasted weather might give them concerns about being able to complete their flight,” he says, “while we have the ability to transition into the IFR system should the weather deteriorate. Depending on the time of year, seasonal weather variations and when flight requests happen to come in, we might complete 10 per cent of our flights using IFR.”

Weighing up VFR and IFR

The main advantage of flying under VFR is that the pilot can go where they want, when they want and determine for themselves how they get there, with no contact with air traffic control unless operating in busy airpsace, so allowing greater freedom. To this end, it is often the first choice for HEMS missions.

“VFR allows you to visually identify obstacles, calculate where the most suitable landing site is, appropriate landing direction and identify particular obstacles that are of particular concern to a HEMS pilot such as power lines and masts,” says Stobo. “The pilot will make a dynamic risk assessment to see if the landing is appropriate, taking into consideration local built-up areas.” He adds: “The decision really is a crude decision because from a medical perspective: the pilot wants to land close to the scene. From a flight safety perspective, the pilot will want to land in a big, clear area as far away from houses and built-up areas as possible. All HEMS launches and certainly HEMS arrivals will be VFR.” 

Biasatti says: “Operating under VFR allows for less planning time, lower fuel requirements and a greater certainty of mission completion.” However, he also adds: “In controlled airspace, other than uncontrolled Class E Airspace, communication [with air traffic control] is required whether VFR or IFR when inside Class D, C, and B. Class A begins at FL180 (18,000 ft) [in the US] and no HEMS operations are conducted that high.”

Meanwhile, the main advantage of IFR is that aircraft can fly in deteriorating weather, meaning that more emergency medical missions can be completed

Meanwhile, the main advantage of IFR is that aircraft can fly in deteriorating weather, meaning that more emergency medical missions can be completed than by using VFR alone. Determining which flight plan to choose is a calculated decision. “Any questions as to my ability to safely complete the flight – taking into account flight time to the patient, ground time, any necessary refuelling stops, return flight time, plus any possible delays – I would always file and fly any one or all legs using the IFR system,” says Biasatti. “Often, we can begin a flight in clear conditions, but upon the return leg the weather has deteriorated or is forecast to deteriorate upon or around our return time, so we may complete part of the flight VFR and another part IFR.”

IFR is ‘very procedural’, says Stobo: “It allows you to fly when the weather’s bad in a wider range of conditions. It extends your operational capabilities. IFR extends the capability of the aircraft so you can operate in multiple types of conditions.”

The real strength of IFR, continues Stobo, is where the pilot goes when recovering from the HEMS mission: “Once they have lifted up with the patient, they are generally going back to major urban conurbations where there’ll be an airport and a runway. So, if the weather’s poor or if it’s night he or she can lift. Whereas if they weren’t instrument rated, they wouldn’t be able to do it. The real boon of the IFR flight is that they can then recover to hospitals and that’s when you’ll find HEMS and air ambulance transfers using IFR.”

Flying under IFR requires a meticulous evaluation of the weather and a detailed flight plan based on route, time, distance, speed, and altitude. There is reliance on air traffic control that separates the IRF aircraft from objects using flight clearance. However, the ultimate responsibility of the safety of the flight remains with the pilot who can refuse clearances. Also, while a pilot may be able to fly through the clouds in IFR legally and safely, there are still minimum weather conditions that must be met before an IFR flight can go ahead. Stobo explains that in UK HEMS, not many aircraft have clearance to fly in icy conditions – generally smaller craft ice up very quickly and that icing is a ‘considerable issue when flying IFR in a helicopter’ and so one of its limitations.

Radio calls, pegging altitude, making complex calculations – flying under IFR is extra workload for the pilot. “It is a much more demanding skillset – especially single pilot IFR,” explains Stobo. “It’s complex, it takes a lot of thought from the pilot, a lot of thinking and risk assessment. Under single-pilot IFR there is a lot of responsibility that remains with the pilot. The challenges are extensive.”