Managing low-visibility procedures like Santa.
Once upon a Christmas Eve flurry, RVR’s were squat; reporting six, four and blurry. “Our Christmas hustle must go on without pause; we can’t wait for the weather,” exclaimed Mrs. Claus. Santa’s retort, was precise and quite short: “I work like a dog, when there’s snow or thick fog. Any bright lights, Christmas trees or red nose, will diffuse in the snow; it’s best I don’t go.”
But the elves had worked hard to empty the shelves, all eight reindeer well fed, were attached to the sled. The children had been good, this was well understood; everyone knew, what Santa simply must do. But the TAF we all know, predicted more heavy snow; his all-nighter flight, would be no delight. With VOR and red nose, though high-tech for a sleigh, without an ILS, there was simply no way.
Not his flawless approach, nor that glowing red snout, helped Santa to land; or to even break out. The missed and divert showed Santa’s pilot skills: dodging chimneys at first, then hill after hill.
Well, I’m sure Santa hated to disappoint all of the children Christmas morning, and he likely got an earful from Mrs. Claus when he called from his diversion hotel in Cabo…I’m just saying. But the mins are the mins, and without the right equipment on the ground and in the air, as well as proper training and proficiency, RVR’s of six, four and blurry are a show-stopper. Especially for eight flying reindeer and a sleigh, with or without a glowing red nose.
In 1929, Jimmy Doolittle became the first pilot to land an aircraft solely by reference to instruments. Since then, we’ve made giant strides in “low visibility procedures,” thereby minimizing the times we go missed or divert due to weather. It began with developing aircraft and ground systems, hardware and procedures, then qualification training and practice in order to fly non-precision approaches in the clouds. Eventually, inflight and ground systems were improved to the point we can now takeoff and land with visibilities measured in just a few hundred feet. Along this journey we found that once we land following a low-visibility approach, or try to leave after refueling, it could be difficult or impossible to find our way. Additional systems and procedures had to be developed to get us from the ramp or gate to the departure runway, or to our parking spot after landing.
The primary ground equipment used in establishing which low-visibility procedures (LPV’s) are in effect is the transmissometer. Transmissometers are used to measure the extinction coefficient of the atmosphere and to determine visual range. They operate by sending a narrow, collimated beam of energy, usually a laser, through the propagation medium. In Santa’s case, snow and fog were the offending “propagation medium.” The measurements are taken at either one, two, three or sometimes four (KDEN), locations along the runway. These positions are classified as touchdown, mid (midfield), rollout and far-end.
The result is expressed as runway visual range, or RVR, in hundreds of feet or meters. Depending on which LVP is in use, we need a specified minimum number of transmissometers to report (that is, functioning), and the value reported must meet or exceed charted RVR minimums in order to use the desired LVP. Individual operators (through FAA ops specs), or the charted procedure itself, may allow substitution of certain transmissometers for another when one or more are inoperative. For example, the mid substituted for touchdown, or far-end for rollout. In order to review several types of LVP’s, let’s take a flight starting from the ramp, a taxi and takeoff, with a review of the decision to return or divert if we have an issue after takeoff, followed by descent and an approach.
First, we need to determine if the visibility is adequate for taxi, takeoff and a return. While Part 91 operators may depart with no visibility constraints, self-imposing the published takeoff minimums found on the airport diagram pages is a good idea. These charts may specify how many, and which, transmissometers are available for each runway as well as RVR values required for takeoff. These visibilities, however, are normally well below Category I landing minimums. After takeoff, if we have the required equipment operating – two motors, electrical and hydraulic systems for example, as well as necessary ground equipment and lighting – a return for a Cat II or III approach may be possible. If we’re not able to perform a Cat II or III landing at our departure airport, then a diversion to better weather, like Santa, rather than back to the six, four and blurry airport we just left, would be the plan.
Therefore, when the takeoff visibility is below Cat I mins, select a takeoff alternate within a prudent distance that would allow you, the airplane and your avionics to fly a single-engine, Cat I approach. A piston twin may not have the ability to fly single-engine to another airport with better weather. If not, then waiting for the takeoff weather to reach Cat I landing minimums would be another prudent, self-imposed restriction.
SMGCS, REL’s, THL’s, SMR and ASSC
Next, review the SMGCS (Surface Movement Guidance Control System) taxi procedure pages. There will be charts for several visibilities to and from the active runway (Less than RVR 1,200 to 600, or RVR 600 to 300, for example). Using in-ground, multi-color lights similar to the runway centerline lights, the charts will depict a unidirectional or bidirectional route, geographic position markings, holding “bars” as well as Runway Entrance Lights and Takeoff Hold Lights (REL’s and THL’s) to the takeoff runway.
Since we seldom use these charts, a slow and thorough review before engine start should be accomplished. While we taxi, ATC will normally monitor surface movement using both SMR (Surface Movement Radar) and the ASSC system (Airport Surface Surveillance Capability). These tools display aircraft and ground vehicles on the airport surface, as well as aircraft on approach and departure paths within a few miles of the airport. Some airports may also offer “follow me” services during SMGCS use. Make sure your transponder is turned on for taxi and don’t forget to enable the “own-ship” display option on your avionics or tablet.
When anticipating a precision approach when visibilities are squat, whether Cat I, II or III, an early review of the descend-via arrival, the approach chart and the arrival SMGCS should be accomplished before the top of descent. Like a puzzle where you try to find a list of hidden objects in a drawing, ball notes and conditional statements are scattered everywhere. In addition to speed and altitude restrictions over each fix, some descend-via procedures will hide a note that tells you to maintain 280 kts when transitioning from mach, for example.
On the approach chart, requirements for visibility, approach and runway lighting, radar, GPS or DME, minimums when the arrival field altimeter setting is not available and often times, a convoluted missed approach or obstacle avoidance procedures must all be reviewed and understood. Look for notes that say special aircrew (SA) training or onboard equipment is required (i.e., Flight Director, autopilot or HUD), changes to approach legality “with ships taller than 144 feet present; procedure not authorized” (KBOS, ILS 4R), or a note that may say the localizer is not accurate certain distances off the course centerline or unusable during landing rollout.
Check the NOTAM’s and ATIS for inoperative approach-related ground equipment. Then, during the approach, aircraft systems as well as airport lighting and transmissometer functionality should be monitored. Depending on which airborne or ground equipment fails or drops below minimums, different operators may allow continuing after glide slope intercept, or may require a go-around (rejected landing).
And finally, after landing rollout we may be back to yet another SMGCS chart where there will undoubtedly be differences from the departure SMGCS, including another ball note search-puzzle. Like Santa said, with snow or thick fog, we will work like a dog.
Missing Christmas or an important commitment because of weather is something that we all face. But having the right equipment, procedures, knowledge and proficiency will increase the likelihood of landing at our planned destination. None of us want to disappoint family, friends or our passengers, nor get an earful from Mrs. Claus.
How do we prepare for our own “One Foggy Night?”
Talk to the weather man, your crew and the dispatcher, too. Hear all of their words, until they are through. Once in the fog we will work like a dog, so try not to hurry when the airport gets blurry. Learn ILS’s, RVR’s and airport SMGCS, too. Follow the charts, hidden ball notes all through. Study and practice, till our faces turn blue; and stay on the gauges, that’s what we must do. Though whine and complain the passengers may chide, good judgment prevails and we must decide: do we fly the trip with caution astride, or cancel the flight and stay home inside.
Be diligent and careful out there my friends.