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Gone cruising: in the real world of IFR flying, the visual approach rules the day. But sometimes, no approach is even better.

We were preparing for our semi-annual fishing trip to Lake Ouachita, in Arkansas's Ouachita National Forest. We shoot the ILS into Hot Springs when weather precludes a visual approach at Mount Ida (a.k.a., Bearce or 7M3). But Jeb, our fishing guide, always gives us a hard time. "Looked to me like you could've landed at the Mount," says Jeb, "and saved me the long drive into that big ol' city of Hot Springs."

I don't feel pressured by Jeb to change my flying habits, but I started wondering about airports like Mount Ida that have no IAP. I did some checking and realized that a cruise clearance could get me to the Mount when the weather was OK, but too low for a visual approach. That would keep Jeb quiet and give me extra time to land the big one--if the weather wasn't too bad and I played my cards right.

You Rule

The word "cruise" within the ATC system dates back to at least 1952. It's morphed over the years and is now defined in the Pilot/Controller Glossary as:

Used in an ATC clearance to authorize a pilot to conduct flight at any altitude from the minimum IFR altitude up to and including the altitude specified in the clearance. The pilot may level off at any intermediate altitude within the block of airspace. Climb/descent within the block is to be made at the discretion of the pilot. However, once the pilot starts descent and verbally reports leaving an altitude in the block, he/she may not return to that altitude without additional ATC clearance.

Further, it is approval for the pilot to proceed to and make an approach at destination airport and can be used in conjunction with:

a. An airport clearance limit at locations with a standard/special instrument approach procedure. The CFRs require that if an instrument letdown to an airport is necessary, the pilot shall make the letdown in accordance with a standard/special instrument approach procedure for that airport, or

b. An airport clearance limit at locations that are within/below/outside controlled airspace and without a standard/special instrument approach procedure. Such a clearance is NOT AUTHORIZATION for the pilot to descend under IFR conditions below the minimum IFR altitude nor does it imply that ATC is exercising control over aircraft in Class G airspace; however, it provides a means for the aircraft to proceed to destination airport, descend, and land in accordance with applicable CFRs governing VFR flight operations. Also, this provides search and rescue protection until such time as the IFR flight plan is closed.

Perhaps no other ATC clearance gives a pilot so much latitude coupled with broad discretionary powers as the cruise clearance. Yet it's rarely mentioned in Instrument training. My logbooks don't show a single entry where I received training in--nor instructed my students in--the art of the cruise clearance. It wasn't part of the curriculum.

I checked two current IFR training manuals and cruise clearances and procedures were wanting. My 1967 Jeppesen Instrument Rating Course briefly mentions cruise but doesn't explain how to actually prepare for and conduct a cruise clearance. Had I not been an en route controller at the time I could not have known what Jeppesen was talking about. Likewise, the controller handbook and AIM ignore its significance for the most part. AIM only mentions it in the Pilot/Controller Glossary. The FARs completely ignore the subject. The only place it's mentioned in the controller bible in addition to the Pilot/Controller Glossary is in Chapter 4, Section 5, Altitude Assignment and Verification. An odd classification for what is essentially an approach to an airport. I think it should be listed under Section 8, Approach Clearance. However, the location is not as important as what it says.

4-5-7 Altitude Information states:

a. Altitude to maintain or cruise. When issuing cruise in conjunction with an airport clearance limit and an unpublished route will be used, issue an appropriate crossing altitude to ensure terrain clearance until the aircraft reaches a fix, point, or route where the altitude information is available to the pilot. When issuing a cruise clearance to an airport which does not have a published instrument approach, a cruise clearance without a crossing restriction may be used.

Note 2. When an aircraft is issued a cruise clearance to an airport which does not have a published instrument approach procedure, it is not possible to satisfy the requirement for crossing altitude that will ensure terrain clearance until the aircraft reaches a fix, point, or route where altitude information is available to the pilot. Under these conditions, a cruise clearance without a crossing restriction authorizes a pilot to determine the minimum IFR altitude as prescribed in 14 CFR Section 91.177 and descend to it at pilot discretion if it is lower than the altitude specified in the cruise clearance.

This paragraph probably should be printed in the AIM for pilot education and use.

There's little advantage to a cruise clearance at airports with an IAP, unless you're conducting training flights to multiple airports. Without a published approach, however, the controller is limited to the minimum instrument altitude (MIA) or the minimum vectoring altitude (MVA) when vectoring you for the visual. This may be higher than the legal minimum instrument altitude--which is yours for the taking with a cruise clearance.

The Hybrid Approach

The evening before our trip I reviewed the requisites for the cruise clearance into Mount Ida and alternatives should the weather be uncooperative. FAR 91.177 says I can descend to an altitude 1000 feet above the highest obstacle within four miles either side of my course in non-mountainous areas.

Although Magazine Mountain is 2753 feet MSL, the AIM does not designate the Ozarks as mountainous. I'll file direct Hot Springs then direct Mount Ida, which is located on the 271 radial of the Hot Spring VOR (HOT) at 21.8 miles.

Plotting the eight-mile route to Mount Ida on the Memphis Sectional Chart, it looked like the highest terrain was 1550 feet MSL and the highest antenna was 1634 feet MSL within our protected corridor. The 2029-foot antenna located five miles southwest of Mount Ida was not a factor since we'd make a right climbing turn if we went missed approach.

Now I know my MDA is 2634 feet or approximately 2000 feet above the Mount Ida airport. The forecast for Hot Springs at our arrival time is ceiling slightly higher than 2500 feet or 3040 feet MSL and visibility six miles. If this forecast is correct, I should break out approximately 3000 feet on my way to 2634 feet.

Homemade Missed?

Next I make plans as to what I'll do in event the forecast is a bummer. Technically there is not a missed approach for a cruise clearance. Our clearance limit is Mount Ida. However, controllers will protect the appropriate airspace until receiving a cancellation or a request for a revised clearance.

Although pilots are not required to know what size holding pattern a controller protects in a non-radar environment, controllers generally protect an area six miles beyond the clearance limit, seven miles on the turn side, 10 miles for the outbound leg, and five miles on the non-turn side. ATC is authorized to hold two aircraft at the same altitude as long as these holding pattern airspaces do not overlap. They can touch, but not overlap.

Here's where an important part of the cruise definition comes into play. It states that "once the pilot starts descent and verbally reports leaving an altitude block, he/she may not return to that altitude without additional ATC clearance."

The key words are "verbally reports." I don't know of a case where a controller asked a pilot to report leaving an altitude in descent when cleared to cruise but I suppose it could happen. The reason is the controller normally uses the MIA for the top of the block and the pilot determines the altitude for the lower portion.

Don't give away the farm. This top or cruising altitude is available for a missed approach altitude as long as you don't sing like a bird and give it back to the controller. When ATC clears you for a cruise clearance, jot the altitude down just like any other clearance. You'll need it in case of a missed approach.

When it came time for the approach, the controller would clear me to cruise at 4300 feet. That would provide me with a vertical block of airspace from 2634 feet up to and including 4300 feet. If I wasn't in VFR conditions at the HOT 20 DME fix I would make a right climbing turn to 4300, enter a standard holding pattern east of the HOT 271 radial at 20 miles and obtain another clearance from Memphis Center.

Pilots don't have access to en route controller MIA charts and have no real need for them. Normally the minimum IFR altitude determined by the pilot will be lower then the controller's MIA. For instance, the MIA over Mount Ida is 4300 feet.

The reason is the MIA covers a much larger geographical area then our cruise corridor. The 4300-foot MIA over Mount Ida extends approximately 47 miles north to the SCRAN intersection, and much higher terrain. Slicing the designated areas into smaller pieces would lower the MIA in some segments but wouldn't be practical due to increased clutter on the MDM display and the increased difficulty for the controller to transpose the data.

Keeping Jeb Happy

On the day of reckoning, sure enough, the weather was too low for a visual but looked good for a my home-grown approach based on the cruise clearance.

After a radar handoff and communications change by Little Rock Approach to Memphis Center I contacted Memphis and advised we had the Hot Springs ASOS. I was issued descent from 8000 to 5000 feet. While over HOT, I overheard an inbound to Hot Springs (KHOT) cancel, then Center transmitted: "Cessna One Victor Echo, cleared to Mount Ida, cruise 4300, change to advisory frequency approved."

Thirteen miles west of HOT I broke out at 2900 feet, with Lake Ouachita beckoning at two o'clock. As I taxied up to the ramp, Jeb waved, a huge grin on his face, glad he didn't have to pick us up in that "big ol' city of Hot Springs."

Charles D. Richardson is a retired controller, who goes fishing in his son's Cessna 210.


How well do you know that four-stroke beast hauling around your light single? We got cranky A&P/IA Mike Busch on the line this month to find out. You can find Mike at and the answers on page 20.

1. The digital engine monitor in your single-engine Cessna shows cylinder #1 with a substantially higher CHT reading than the others. Which is cylinder #1?

a. The rear cylinder on the right side of the engine.

b. The front cylinder on the left side of the engine.

c. The front cylinder on the right side of the engine.

d. Either (a) or (c) depending on the model of Cessna.

2. While cruising at 12,000 feet in your TCM O-470-equipped Skylane, you notice that the rear cylinders are considerably hotter than the front cylinders. It's a clear winter day with the cowl flaps closed and the cabin heat on. What's up?

a. The O-470's front cylinders naturally get more cooling air than the rear cylinders because they don't have anything in front of them to block the air flow.

b. There's something wrong with your rigid cooling baffles and/or flexible baffle seals.

c. The front cylinders naturally run richer than the rear cylinders due to the design of the induction system.

d. You should be concerned about an exhaust leak.

3. What action (if any) could you take to help equalize the CHTs on that Skylane's O-470 powerplant?

a. Apply partial carburetor heat.

b. Open the cowl flaps halfway.

c. Operate lean-of-peak (LOP).

d. Land and ask your mechanic to find and fix the problem.

4. Your oil temperature shows about 190 degrees F in cruise. The green arc on the gauge extends from 70 degrees F to 240 degrees F, with a red radial at 240 degrees F. Everything is OK, right?

a. Yup. In fact, 190 degrees F is just about ideal.

b. Although oil temp is in the green, a reading of 215 degrees F or higher is preferable to purge moisture and minimize corrosion. (It takes 212 degrees F to boil water.)

c. Although oil temp is in the green, a reading of 165 degrees F or lower reduces oxidation of oil additives.

d. Although oil temp is in the green, a reading of 165 degrees F or lower is preferable because it improves engine cooling.

5. The TCM TSIO-550-G engine in your new Mooney Acclaim is at 65-percent cruise power. If you slowly move the mixture control from full-rich to almost-too-lean-to-run, in what order would you expect the following events to occur?

a. Best Power, Peak EGT, Best Economy, Maximum CHT

b. Best Power, Maximum CHT, Peak EGT, Best Economy

c. Best Power, Peak EGT, Maximum CHT, Best Economy

d. Maximum CHT, Peak EGT, Best Power, Best Economy

6. You accidentally back your Porche 911 Targa into the Mooney's three-bladed prop. You were only going about two mph at impact, but it put a slight bend in one of the prop blades. What should you do?

a. Ask your mechanic to try to straighten the blade. Since the engine wasn't running, there was no "sudden stoppage" and don't have to do a costly teardown inspection.

b. Ask your mechanic to remove your prop and send it to the prop shop, and then use a dial indicator to measure the runout of the crankshaft prop flange. If the flange runout is within specs, you don't have to do a teardown inspection.

c. Ask your mechanic to send your prop to the prop shop, and your engine to the engine shop for a teardown inspection. It'll cost a bundle, but that's why you have hull insurance.

d. Never mind the airplane, you dented the Porsche!

7. Both Lycoming and TCM publish specific "time between overhaul" (TBO) figures for each engine model they produce. Operating beyond published TBO is

a. in violation of 14 CFR [section]91.417(a)(2)(iii).

b. not in violation of FAA regulations, but if you have an engine-failure incident, your insurance may deny coverage.

c. not in violation of FAA regulations, but in-flight engine failures beyond TBO are statistically more likely.

d. not in violation of FAA regulations, and may reduce maintenance expense without compromising safety.

8. You're listening to the XM satellite radio Beatles marathon when you notice that the EGT on your #4 cylinder has risen by 50 degrees F, while the CHT has dropped by a similar amount. What now?

a. It's a partially clogged fuel injector. Shove the mixture full-rich, and if that doesn't help, try the boost pump. Land as soon as practicable to avoid cylinder damage.

b. It's a non-firing spark plug. Do a mag check to determine whether the top or bottom spark plug is the culprit. Continue to your destination, and have the plug changed.

c. It's detonation! Throttle back immediately, land as soon as practicable, and have the cylinder borescoped.

d. It's nothing to worry about. EGT variations of 50 degrees F are commonplace. Enjoy the music and ignore the reading.

9. If the maximum oil capacity of a six-cylinder, wet-sump, piston, aircraft engine is 12 quarts, what is the minimum oil level needed to ensure proper engine operation in all normal flight attitudes and atmospheric conditions?

a. 6 quarts.

b. 7 quarts.

c. 8 quarts.

d. 9 quarts.


1. d. It depends on whether your Cessna has a Lycoming or Continental engine. On a Lycoming engine, #1 refers to the right front cylinder; on a Continental engine, #1 refers to the right rear cylinder.

2. c. The fuel-air mixture from the carburetor has to make a right-angle turn in the TCM O-470, which the air has no trouble doing, but the suspended fuel droplets don't like. Consequently, the rear cylinders get less than their fair share of fuel, and the front cylinders get more than their fair share. This shows up on the engine monitor as a CHT imbalance.

3. a. A touch of carb heat improves fuel atomization and reduces droplet size. This makes it much easier for the fuel droplets to turn corners as they flow through the induction plumbing. If you use this technique, having a carburetor air temperature gauge is quite helpful in determining when and how much carb heat to apply.

4. a. An oil temperature gauge reading of 180-200 degrees F is optimal. The temperature probe is usually mounted near the oil cooler outlet and measures oil temperature at the coldest part of its cycle. Peak oil temperature is usually about 40 degrees F, higher than what is on the gauge. A peak temp of 220-240 degrees F is hot enough to purge embedded moisture, but not hot enough to cause accelerated oxidation of the oil and its additives.

5. b. Best power typically occurs at about 125 degrees rich of peak EGT (ROP). Best economy is achieved with a mixture that is lean of peak EGT (LOP). Maximum CHT occurs at about 40 degrees F ROP, but steer well clear of that mixture setting any time power is greater than 65 percent. At higher power settings, it's best to operate either LOP or very ROP.

6. c. Your A&P mechanic cannot legally try to straighten your prop blade (14 CFR [section]65.81), and both TCM and Lycoming require an engine teardown inspection after any propeller damage that necessitates propeller removal even if the engine was not running (TCM Service Bulletin 96-11A, Lycoming Service Bulletin 533). Not only will your insurance pay for the teardown inspection but they might not renew coverage without it. (Yes, this has happened.)

7. d. Lycoming and TCM publish service bulletins containing recommended engine TBOs, but these are purely advisory and not considered to be limitations. Even if that were not true, Part 91 operators are not required to comply with manufacturer's service bulletins and Part 135 operators routinely get FSDO permission to exceed TBO.

8. b. A helpful rule is that ignition-related problems usually cause EGT and CHT to move in opposite directions while fuel-related problems usually cause EGT and CHT to move in the same direction (whether you're ROP or LOP).

9. a. See 14 CFR [section]33.39(a): "The lubrication system of the engine must be designed and constructed so that it will function properly in all flight attitudes and atmospheric conditions in which the airplane is expected to operate. In wet sump engines, this requirement must be met when only one-half of the maximum lubricant supply is in the engine."
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Title Annotation:Instrument Flight Rules
Author:Richardson, Charles D.
Date:Nov 1, 2006
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