IFR: Flight at Mid-Level Altitudes

Today we’re pleased to feature a guest post from CFI and DPE Jason Blair. Check out his previous contributions to the LTFB here. He writes his own blog at

Learning to fly in IFR conditions requires a great deal of study and skill development. Flying blind isn’t easy! But general instrument flight training typically focuses on low level flying skills, in effect, the basic building blocks of instrument flying that include basic flying skills, enroute navigation, and approach procedures. For many pilots, this is as far as their instrument flying goes. For professional pilots and pilots who seek to transition into bigger, faster, and higher-flying aircraft some knowledge gets skipped in the initial training that will be useful as they expand their flying envelopes. Transitioning to flying aircraft that fly at higher altitudes requires the development of some additional instrument pilot skills and awareness of additional procedures.

IFR flying at mid-level altitudes, such as above the oxygen requirements of 12,000’ MSL through approximately 25,000’ MSL, is between the altitudes that many general aviation aircraft fly and the altitudes that most jets fly (mostly over 30,000’ MSL). This is regularly accomplished in aircraft such as Cessna 414’s and 421’s, Piper Cheyennes, and King Airs to name only a few. These aircraft are typically pressurized, can climb to altitudes that most light GA aircraft cannot reach, go faster, and are regularly owner flown. While these flights may not require all of the same operational planning that higher jet flights do, some things do go beyond the basic IFR training that a pilot transitioning into these mid-level altitudes should consider.

High Altitude Enroute Charts
Most IFR training is conducted using low-altitude enroute charts, and take into consideration things like MEAs, MOCAs, and VOR airways during planning. As pilots fly higher, the use of high-altitude enroute charts becomes prudent and necessary for flight above 18,000’ MSL. Familiarization with high-altitude enroute charts has become easier than it was historically as more pilots transition to using digital EFB apps for their charting. Most applications allow the pilot to easily switch between high- and low-altitude enroute charts.

Some key points about high-altitude enroute charts:

  • “Terminal” VORs are not depicted
  • “Low Altitude” VORs will be depicted without a compass rose
  • Localizers are not depicted
  • Victor airways between low-altitude VORs are not depicted

The high-altitude enroute charts are typically used for longer distance planning. While many aircraft are not operating GPS for direct enroute capabilities, if a pilot is planning to use VOR systems, especially when operating off Victor airways, it is important for a pilot to remain aware of VOR service volumes when planning routes.

Planning Ahead for Descents
A descent from 8,000’ MSL to a ground elevation of 1,000’ MSL will happen much faster than one from FL250 to 1000 at the airport. Pilots transitioning to flight at mid-level altitudes will need to develop the skill of planning for a descent further out. This can be a critical planning phase of operating at these altitudes to allow for sufficient time to descent without having to “dive to get down” and risking high rates of descent that can potentially shock cool engines or just be very uncomfortable for any passengers.

Let’s put some math to this.

A pilot flying at 8,000’ that needs to descend to 3,000’ to begin an approach to an airport has to descend 5,000’. If the plan is to descend at 500’ per minute, this will take 10 minutes (5,000/500). A typical general aviation aircraft may fly this descent at 150 knots. During that 10 minutes (⅙ of an hour) the aircraft would travel 25 nautical miles (10/60 minutes x 150 knots).

If a pilot is descending from 25,000’ to 3,000’ to begin an approach to an airport, they have 22,000’ to descend. If a pilot wants to keep a stable descent rate of 500’ per minute, this will take them 44 minutes (22,000/500). If the aircraft is travelling at 200 knots in the descent, and the pilot plans to make the descent for 44 minutes (approximately ¾ of an hour – (44/60 minutes  x 200 knots)) this means that the pilot will have to begin the descent 150 miles away from the airport! If the descent is started any closer than that, either the aircraft will have to be slowed down or the descent rate increased.

The same math can be applied to climbing.

In many cases, it may take 100 or more miles to climb to a cruising altitude and equal or greater distances to plan for a descent. When transitioning to flight at mid-level altitudes, the flight profiles will include much longer climb and descent phases than lower-flying light general aviation aircraft. In some cases, the enroute cruise phase may not be much longer than either of the other phases.

A good general rule in planning is that if the enroute cruising phase is less than ⅓ the time of the entire flight, you have climbed higher than would be efficient over the distance travelled.

Slowing Down as You Go Down
You probably memorized it when you took your IFR knowledge test, but may not have used it since then. With higher-flying aircraft that can build up momentum in a descent, or just fly faster in general, there are times you need to slow down when descending from higher altitudes.

A friend of mine refers to this as “entering the school zone.”

When you “go down” you “slow down.”

FAR §91.117 requires an aircraft to be operated below 250 knots when below 10,000’ MSL and under 200 knots when in Class B, C, or D airspace unless authorized or required by ATC. The good news is that this is “indicated airspeed,” so if you have a tailwind that is helping push your ground speed above the maximums it can be bonus. The number on your airspeed indicator is the one that counts.

Greater Use of Arrival and Departure Procedures
Flying higher, longer distances and with new flight profiles will many times expose a pilot to more frequent use of arrival and departure procedures. These are more common at bigger airports with more traffic, but there is a good chance that if a pilot is flying a bigger, faster, more capable aircraft it is more likely that they will be going to these airports.

Arrival and departure procedures more commonly get assigned to aircraft flying at higher altitudes in an effort to help transition traffic from terminal areas to the enroute “Center” controllers that offer traffic separation and routing above 10,000’ MSL in most areas.

As a pilot expands to higher-altitude flying, these procedures may include altitudes, climb or descent rates, or additional routing that is less frequently experienced in lower-level flight operations.

In general, flying at higher altitudes becomes more procedural. When a pilot flies above FL180 (18,000’ MSL), it is mandatory to be on an IFR flight plan following IFR operational rules. The days of punching in a Direct-To on the GPS and heading out VFR without any additional planning are over.

While there is no doubt more that could be covered, these are a few things that pilots who are transitioning to flight at higher altitudes will need to brush up on or learn if they were not adequately covered in their initial IFR training.

Jason Blair is an active single and multi-engine instructor and FAA Designated Pilot Examiner with 4,800 hours total time and 2,700 hours instruction given. He has served on several FAA/Industry aviation committees and has and continues to work with aviation associations on flight training issues. He also consults on aviation training and regulatory efforts for the general aviation industry.

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