Stable Approach by Design

Normal Procedures

Eddie sez:

When I think back to my last several unstable approaches — I've had a few over the years — there are usually a few reasons behind each. Chances are they were caused by: (1) actions by other aircraft, (2) actions by ATC, (3) actions by sudden weather changes, or (4) actions internal to my aircraft, in other words, me. While there are things we can do to shape the outcomes and perhaps the inciting events of (1), (2), and (3), they are for the most part outside our control. The last item, however, are within our grasp of control. Or are they?

There is much written about how to wire in the correct vertical and horizontal parameters, how to combat pilot continuation bias, and normalizing the go around decision. In fact, I do that here: Stabilized Approach.

But there is another facet of this problem that hardly gets any discussion at all: checklist design. I heard of a Hawker Before Landing Checklist with 16 items on it, 15 of those after the gear is extended. If the pilots are busy ticking off 15 things to do just a minute or so prior to landing, how much effort is left to keep things, um, stable?

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How much time once the gear is down?

When is the Before Landing Checklist accomplished?

A good time to accomplish the Before Landing Checklist is after the landing gear has been extended and a good time to extend the landing gear is when intercepting the glide slope. Delaying the gear until glide slope intercept can be said to improve approach stability, since adding drag when starting down reduces (or can even eliminate) the need to reduce thrust settings.


Photo: Teterboro Airport (KTEB), New Jersey, ILS 19, profile view
Click photo for a larger image

So how much time does that give you to accomplish any checklists? Looking at the ILS Runway 19 to Teterboro Airport (KTEB), New Jersey can provide a useful working model. Since the runway is a mere 6 feet above sea level, it also makes the math easy. Glide slope intercept happens at 1,500 feet MSL and 4.5 nautical miles from the end of the runway. At a hypothetical approach speed of 120 knots ground speed (to make the match easy), we are traveling at 2 nautical miles per minute, or a nautical mile every 30 seconds. In the example approach, we will have 2 minutes and 15 seconds to accomplish the Before Landing checklist.

But if we are in IMC, we will want to have that done no later than 1,000 feet, giving us only one-third the altitude and one-third the time, so just 45 seconds. Keep in mind the PM should be simultaneously monitoring the approach progress as well as the radios. The PM will also have to look outside with increasing frequency as the descent progresses. Is 45 seconds enough time to accomplish a properly designed checklist?

How should a checklist be designed?


Photo: Boeing Model 299 Crash, 30 Oct 1935, USAF Photo.
Click photo for a larger image

It may seem odd to a modern aviator, but we survived nearly thirty years of aviation without formalized checklists. Doing everything that needed to be done was just a part of the pilot mystique. Starting with the airplane that became the Boeing B-17, we realized there was too much to do to leave it to memory. An early model of that airplane crashed in 1935 when the very competent test pilots forgot to unlock the controls. The design was almost abandoned until the Army Air Corps developed checklists for its crews for takeoff, flight, landing, and after landing. We modern aviators just accept that they are a part of the job. At least most of us accept that.

Are checklists required? 14 CFR 91, §91.503, says we need to have checklists accessible at our "pilot station" for each flight, but not that we necessarily have to use them. You can argue that 14 CFR 91, §91.13, (Careless or reckless operations), compels us to. I would agree with you, but not everyone does.

Regardless of where you stand on the "must use" or "it's optional" question, there is a right way and a wrong way to designing a checklist. While the following from FAA Order 8900.1, Volume 3, Chapter 32 is specifically aimed for 14 CFR Parts 91K, 121, 125, and 135, I think Part 91 operators would be well advised to follow as well.

  • A normal checklist is typically a listing of action items to be performed and verified at a particular point in flight.
  • Most normal procedures do not require itemization or incorporation into a checklist. For example, the procedures for making normal takeoffs and landings are not itemized in a checklist format, but described in a narrative format.
  • Checklists must be kept as short as practical to minimize “heads-down” time and diversion of the crew’s attention while performing the checklist.
  • In technologically advanced aircraft, the same items are accomplished and monitored by automatic systems that relieve the flightcrew of these tasks.
  • For single-pilot aircraft, the FAA recommends that operators mount the before takeoff checklist and the before landing checklist on the instrument panel by means of a placard. When aircraft characteristics allow, the operator should develop touch-verification procedures that contain a requirement that the pilot touch each control to verify it is in the correct position.
  • For two-pilot aircraft in which only the PIC has ground steering control, the recommended method for accomplishing checklists is for the second-in-command (SIC) to read all checklists when the aircraft is in motion on the ground. The recommended method for those aircraft in which either pilot can steer on the ground is for the pilot not flying (PNF) to read all checklists. In all two-pilot aircraft, the PNF should read all checklists when the aircraft is airborne.
  • On approach, flight guidance checklist items have proven to be critical items. At least two crewmembers should confirm and respond to these items. A response should be required from each pilot when the same setting is required on two separate devices (such as computers, flight instruments, or altimeters).
  • Checklists should not be depended on to initiate changes in aircraft configuration. Operators should key aircraft configuration changes to specific operational events. For example, the operator may direct the landing gear to be extended at glideslope intercept.
  • When the operator has a choice as to where an item should be placed on a checklist, it should be placed at a point where the crew workload is lowest.
  • Operators should keep checklists as short as possible in order to minimize interruptions.

More about all of this: Checklist Philosophy.

Manufacturers have wide latitude in checklist design and for the most part look for consistency among aircraft models. Pilots flying multiple types may have added challenges when these designs vary even slightly.

Examples of Before Landing Checklist design


Photo: G150 pilots Dan Hoyberg-Nielsen and Steven Foltz and their checklist
Click photo for a larger image

A poorly designed checklist

Some of the best and worst before landing checklists I've seen come from Gulfstream, here is one from the latter category, the G150.

Before Landing Checklist
  1. Landing Reference Speed (VREF) . . . CONFIRM & SET
  5. APR ARM . . . ARM
  6. Landing Gear . . . DOWN / 3 GREEN
  8. Hydraulic Pressure . . . CHECK MAIN & AUX
  10. Brake Lever . . . OFF
  11. ENGINE SYNC . . . OFF
  12. GROUND A/B . . . LAND
  13. SLATS / FLAPS . . . FLAPS 40°
  14. Autopilot . . . DISENGAGE
What is wrong with it

I think most of us mentally connect the Before Landing Checklist with the act of extending the landing gear; when we get rushed we think "got to put down the gear," followed by "what else?" Hopefully the "what else" is the checklist, but that can become rushed if the checklist is a long one. Looking at the G150 checklist:

  • The five items before landing gear are apt to be forgotten in the heat of battle. Some Gulfstreams (not this one) have an "in range" checklist for these kinds of things that can be taken care of early.
  • If at all possible, the Before Landing Checklist should begin with the landing gear so as to turn the whole thing into a call out: "Gear down, Before Landing Checklist." That makes it less likely you will forget to call for the checklist.
  • At least two of the items after the landing gear can be accomplished before this checklist: brake lever, engine sync.
  • The autopilot item, on an airplane without autoland, should be considered an automatic function of flying the airplane. All of the "traditional" Gulfstreams, those originally designed by Gulfstream, cannot be landed with the autopilot engaged, and yet this checklist item isn't used.
  • The checklist takes an average of 45 seconds to accomplish, so just enough from glide slope intercept to our stable approach height, provided there are no other distractions or demands on the PM's time.

A well designed checklist

The Dassault Falcon 900EXy has an exceptionally well designed Before Landing Checklist, but to appreciate why, you need to look at the checklist that comes before it as well.

  1. Altimeters (all 3) . . . QNH
  2. Approach settings . . . Checked
  3. LANDING lights . . . ON or PULSE
  4. FASTEN BELTS . . . On
  5. NO SMOKING . . . On
  6. Cabin . . . Ready
  7. STATUS page . . . Checked
Before Landing
  1. Landing gear . . . 3 greens
  2. SLATS / FLAPS . . . 40°

It appears Dassault has made a conscious effort to ensure both pilots are not distracted by checklist duties once the gear, slats, and flaps are set for landing. Most aircraft manufacturers fall short of this ideal. Quite often aircraft design drives the checklist.

How does aircraft design impact checklist design to improve the odds of a stable approach?

The G150 Before Landing Checklist provides an object example of how aircraft design drives checklist construction. Even moving the five items that appear before the landing gear and two later items to an earlier checklist, we are still left with five items (anti-skid, hydraulic pressure, thrust reversers, ground a/b, slats/flaps) once the gear is down. These items cannot really be checked until the gear is down.

Con: Interdependent mechanical systems

Three thousand pounds per square inch is almost a universal pressure for aircraft hydraulic systems, providing a lot of muscle from one part of the airplane to others using relatively compact and light-weight tubing. This has been the method of choice for many years when it comes to landing gear, flaps, slats, ground spoilers, and flight controls. A limitation with such a setup is that the fluid under high pressure can deplete itself very quickly when the system develops a leak. One of the most feared scenarios is for a leak in the landing gear to deprive the airplane of flaps, slats, spoilers, and wheel brakes at the last moment of flight. That is why many manufacturers include a last-minute check of those components and the hydraulic systems once the landing gear is extended. You can't do this check beforehand.


Photo: The hydraulics synoptics page from a GVII, (Eddie's aircraft)
Click photo for a larger image

On many aircraft, most of the critical systems that slow the aircraft prior to landing and stop it after are electronically monitored to provide a warning should they fail. Shouldn't this relieve the pilot of the responsibility?

Con: Analog warning systems with reporting lag times

My first large aircraft larger than 12,500 lbs was the KC-135A tanker. At nearly 300,000 lbs., it was large indeed. Designed and built in the fifties, the crew alerting system consisted of two pilots. As a copilot, the blame for missing anything fell on my shoulders. I learned early on to mark all the gauges with a grease pencil so I could, at a glance, detect when something wasn't the way it was hours earlier. It was an imprecise method.

My first airplane with a master caution panel was a Boeing 747-200. It had an array of lights, each connected to an analog switch of some sort along with another light that told me if any of the other lights was triggered. It was magic.


Photo: Cessna Citation Encore master caution panel
Click photo for a larger image

The problem, however, was found in those analog switches. To illustrate, consider the Gulfstream III's master warning light panel. Before we do that, however, remember there is a saying in the GIII world: "If you've flown one Gee Three, you've flown one Gee Three." There are a lot of variations. But in the GIII's that I flew, the warning light on the ninth row, first column was labeled "COMB HYD" and would illuminate in amber if the pressure fell below 800 PSI. The airplane had a part-time 1,500 / 3,000 PSI system that would use the higher pressure with the gear or flaps extended. A drop to 800 PSI may have been enough to detect a large hydraulic system leak in the landing gear but not enough for a small leak in the flaps. So the ninth item after the landing gear in our Before Landing Checklist was to check the hydraulic system pressure on a gauge just forward of his or her inboard knee. It was a checklist item we couldn't give up and that had to appear after the landing gear and flaps.

Pro: Intelligent and quick Crew Alerting Systems

The Gulfstream GVII also has a 3,000 PSI system that drives the landing gear, flaps, and wheel brakes, though it is at 3,000 PSI full time. The pressure sensor feeds directly into a digital network that is monitored continuously for faults. A pressure drop below 2,350 PSI immediately generates a "L Hyd Pump Fail" and if that were accompanied by a quantity loss below 0.3 gallons and further pressure loss below 1600 PSI, it would generate a "L Hyd System Fail" message.


Photo: GVII CAS Example, L Hyd System Fail
Click photo for a larger image

These modern warning systems are ever-vigilant so we don't have to be. The requirement to check the hydraulic system after landing gear and flaps extension has been eliminated on many aircraft.

Pro: Self-populating automatic checklists

When I saw the Falcon 900EXy Before Landing Checklist (gear, flap/slat), I was green with envy. Just two items! Here is the GVII Before Landing Checklist:

  1. Autobrake - As required
  2. Seat Belt / No Smoke Passenger Warning - On
  3. Exterior lights - As required
  4. Landing gear / lights - Down / 3 green
  5. Flaps - Set for Landing
  6. Approach / Landing Airspeeds - Verify

Yes, our checklist is three times as long. (A later version cuts it to four items, still twice as long.) But we do have an ace up our sleeves. Once we get to the checklist, the electronics have already checked off all but one of the items; this is what we will see on our electronic checklist:


Photo: GVII electronic Before Landing Checklist
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How does one fix a broken checklist?


Do you have a broken Before Landing Checklist? If so, it could be that the manufacturer designed it in a way to be consistent with other aircraft in their fleet. Perhaps they gave the design duties to a non-pilot. Or it could be an old checklist design that didn't keep up with aircraft modernization. Whatever the reason, your options to improve what you have could be limited.

If you are flying commercially, your checklist will ultimately have to be approved by your operator and approved or "accepted" by the Principal Operations Inspector. If you are flying under FAR Part 91 you have more latitude, but should review FAA Order 8900.1, Volume 3, Chapter 32 to ensure you adhere to what the FAA will view as best practices.

Back to our G150 Example

If I were king, this is what I would do with the G150 Before Landing Checklist. My first step would be to add an In Range Checklist.

In Range Checklist
  1. Landing Reference Speed (VREF) . . . CONFIRM & SET
  5. ENGINE SYNC . . . OFF
Before Landing Checklist
  1. Landing Gear . . . DOWN / 3 GREEN
  2. APR ARM . . . ARM
  4. GROUND A/B . . . LAND
  6. Hydraulic Pressure . . . CHECK MAIN & AUX
  7. SLATS / FLAPS . . . FLAPS 40°

In my view, the Before Landing Checklist can be improved along those FAA Order 8900 guidelines by:

  • Place all lesser items that do not have to wait for the landing gear and flaps in an earlier "In Range" or "Approach" checklist.
  • Start the Before Landing Checklist with a "event initiating" item, preferably the landing gear.
  • Eliminate items that are simply normal procedures, such as disengaging the autopilot or auto-throttles, if that is normal procedure for your aircraft.

14 CFR 25, Title 14: Aeronautics and Space, Airworthiness Standards: Transport Category Airplanes, Federal Aviation Administration, Department of Transportation

14 CFR 91, Title 14: Aeronautics and Space, General Operating and Flight Rules, Federal Aviation Administration, Department of Transportation

14 CFR 135, Title 14: Aeronautics and Space, Operating Requirements: Commuter and On Demand Operations and Rules Governing Persons on Board Such Aircraft, Federal Aviation Administration, Department of Transportation

FAA Order 8900.1 Vol 3 Ch 32, Manuals, Procedures, and Checklists for 14 CFR Parts 91K, 121, 125, and 135.