Instrument Insights Part 9 of 12

Partial-Panel Emergencies

September 1, 1998

Vacuum pump failure is a pop quiz on rusty instrument skills

VFR and IFR pilots alike can experience partial-panel emergencies. Traditionally, a partial-panel emergency results from failure of the aircraft's vacuum pump and the subsequent loss of the attitude indicator and heading indicator.

It can, however, include loss of other instruments such as the airspeed indicator, as any pilot who forgot to remove the pitot cover during preflight can attest. It can also involve electrically powered HSIs and turn coordinators. The type of emergency that you might have depends on how your aircraft is equipped. Your reaction to it depends on how recently you have practiced partial-panel flight.

Bruce Edsten, a former flight school owner who is now with the FAA in the Louisville, Kentucky, Flight Standards District Office, has had only one actual partial-panel emergency in 6,200 hours of flying. It occurred during a training flight. On an otherwise VFR day, the student had filed for an altitude that would put the flight in the clouds, just for practice. The flight was supposed to end with an instrument approach at a Seattle-area airport after a short cross-country flight.

"We heard a noise, the noise stopped, and we had no vacuum pump," Edsten said. The student was caught unaware by this actual emergency and put the aircraft in a slow spiral, following the directions of the dying attitude indicator and heading indicator.

Cross-checking the instruments against one another to see if they agreed would have prevented the student's problem. For example, if the attitude indicator shows 10 degrees pitch down, yet the altimeter and vertical speed indicator show no descent, the attitude indicator may be lying to you. (As a matter of routine, pilots on cross-country flights should check the heading indicator against the compass every 15 minutes and reset it as necessary. If the error seems excessive during one of those checks, it could mean a vacuum or pressure pump failure is in the making.)

Edsten solved the problem by pointing out the failed instruments to the student, who then stabilized the aircraft and reported the situation to air traffic control per FAR 91.187. ATC then granted a descent to VFR conditions and a return to the home airport. Edsten could have asked for "no-gyro" vectors, in which the controller simply says "turn left" and "turn right," ending with "stop turn" when the aircraft is on the correct heading. He might also have asked the controller for the nearest airport with an airport surveillance radar (ASR) approach if there had been no VFR weather near.

Edsten's experience of only one failure in 6,200 hours is by no means typical. Lexington, Kentucky, flight instructor Arlynn McMahon warns students to expect a vacuum pump failure every 500 hours of use. A partial-panel emergency should be considered as serious as losing a magneto, and the proper reaction is to get the aircraft on the ground.

Partial panel work on the instrument checkride

Bill Baumheuter, a designated examiner based at St. Louis Downtown-Parks Airport in Cahokia, Illinois, has noticed a few problems on instrument checkrides. He gives partial-panel exercises twice — once during unusual-attitude recoveries, and again during a nonprecision approach.

Fortunately, most students do well on the partial-panel nonprecision approach. However, one applicant failed after Baumheuter pulled the circuit breaker for the electrically powered horizontal situation indicator (HSI). The HSI froze, and so did the student. The problem was that the student had practiced only simulated emergencies; in his mind, if his flight instructor did not cover the instrument, there was no emergency. When the HSI froze, the student continued on what he thought was a straight course, despite the presence of a little red "HDG" flag on the HSI. Actually, he was turning. That sudden freeze-up is the way the HSI might actually fail someday, but the applicant later complained that pulling the circuit breaker was unfair. Now Baumheuter has gone back to just covering up the two primary gyroscopic instruments.

Designated examiner Bob Gawler of Gaithersburg, Maryland, who is a guest speaker for AOPA Air Safety Foundation flight instructor refresher clinics, saw another problem during a checkride. Gawler waited to cover up the gyroscopic instruments until the student was faced with a high workload during a VOR approach. The student was in the process of intercepting the inbound course, descending from 4,000 feet to 3,500 feet, turning to a new heading, and resetting the clock. The applicant was overloaded with the addition of a partial-panel emergency and missed the turn to the final approach course.

Gawler found that 83 percent of instrument checkride applicants in his geographic area pass the first time. But among those who failed, the leading causes were, in order, the NDB approach, the ILS approach, the VOR approach, en route procedures, and finally, emergency procedures including partial-panel work.

Timed turns, not compass turns

Professional Instrument Courses, based in Essex, Connecticut, sends instructors around the country to train customers for the instrument rating, usually in the student's own aircraft (or a rental aircraft). The school also gives multiengine and commercial training, as well as instrument refresher courses, but it is best known for its 10-day instrument course. Officials agreed to share a few secrets they have learned over the years. Erik C. Lunde, operations manager and an instructor, said that compass turns are good for demonstrations, but not for in-flight emergencies. "We use timed turns — rarely compass turns," he said.

Compass turns require knowledge of that instrument's little quirks. When turning to north or south headings, the compass has a lag/lead error that is equal to the latitude; there are acceleration/deceleration errors as well. The training company warns in its textbook The Instrument Flight Training Manual that all compasses vary in the amount of error they exhibit.

The problems PIC instructors see come from students who don't have confidence in the timed turn and who roll out too early or too late because they have not been timing. Some students won't let the compass settle down before making course adjustments. They end up making S-turns along a radial. "Rely on the clock and maintain a standard-rate [three degrees per second] turn," Lunde said. "Use the aircraft clock on large turns. On small ones, count to yourself. On an ILS localizer, use half-standard-rate turns for corrections."

PIC teaches students to use the compass rose behind the ADF needle, which has tick marks every 30 degrees, and to count 10 seconds for every tick mark between the present and desired heading. If it is a large turn, count 30 seconds for every 90 degrees. That gives students a rough estimate, and they can then count off any leftover degrees.

"We see an awful lot of turn needles [in the turn coordinator] not giving a standard-rate turn. We tell the client he needs to calibrate the instrument," Lunde said. Kentucky flight instructor McMahon adds that most of the client aircraft she has seen have improperly calibrated turn coordinators. She helps the pilots to figure out how to compensate for the error in their particular instrument.

Military and airline perspectives

Ask flight instructors at Laughlin Air Force Base in Del Rio, Texas, how they teach partial-panel flying to fighter pilots, and they'll nearly laugh. "It is extremely rare that you would not have viable instruments to fly off of," says a T-38 instructor. The emergency that comes closest to partial panel failure is called "right generator failure with no crossover." The generator fails, there is no crossover AC power available for the aircraft situation display, and the pilot simply moves his eyes to the DC-powered standby attitude indicator that is already running. That's it. The emergency is over.

"At that point, in-flight guides and checklists take you by the hand to help you try to restart the main display," the instructor said. "There are multiple generators. The military is big on backups and has backup systems to the backup systems. They are also big on systems knowledge."

Boeing 747-400 first officer Sylvia J. Otypka told much the same story about glass-cockpit airline flying. "We are pretty well backed up and partial panel isn't a problem. On a rare occasion, we do practice flying with a loss of some part of our PFD [primary flight display]. As a general rule, though, we do not practice partial-panel approaches regularly," Otypka said.

The 747-400 that she flies has backup power circuits for each pilot. If all of those fail, the battery for the auxiliary power unit can run the cockpit for 30 minutes. "In addition to all that, we still have the standard third set of gauges in the center of the console, with all the primary round-dial instruments just like in the older airliners," Otypka said.

There are lessons from the airlines and the military for general aviation pilots. One is to install the backup systems that you can afford to avoid a partial panel problem in the first place. The options are to purchase a backup pressure or vacuum pump, and a standby alternator or generator. The systems cost less than you might expect. Precise Flight Inc., of Bend, Oregon, offers a standby vacuum system for $429.

Tip Sheet

  • Professional Instrument Courses suggests that you know the configurations that give the performance you need for climb, cruise, cruise descent, approach, approach descent, and nonprecision descent, to ease your workload during partial-panel flight.
  • PIC tells its instructors to have students do some partial-panel work on every flight. That's good advice for the instrument-current pilot, too. If you have a safety pilot, try it during en route portions of a routine flight.
  • Sheri Coin Marshall, FAA Southern Region 1998 Flight Instructor of the Year, uses sticky notes to cover the failed instruments, and then goes one step further. "My students hate partial panel, so I draw a happy face on the sticky note. It sounds silly, but it works. If you get a failure in real life, do the same thing," she advises.
  • Use cockpit resource management, says Lexington, Kentucky, flight instructor Arlynn McMahon. At Aero-Tech, she tells students to remember that they have an autopilot on board. If it won't work in Heading mode, because the heading indicator or turn coordinator has failed, maybe it will control the aircraft in Nav mode. If the aircraft has an ADF with a moving compass card — one that is slaved to a magnetic heading sensor — use it as a replacement for the heading indicator.

Links to all Web sites referenced in this issue can be found on AOPA Online ( www.aopa.org/pilot/links.shtml).

For additional information, visit the Professional Instrument Courses Web site ( www.iflyifr.com). Contact Sylvia Otypka at Leading Edge Publishing, Post Office Box 461605, Aurora, Colorado 80046-1605. Write to Precise Flight Incorporated at 63120 Powell Butte Road, Bend, Oregon 97701; telephone 800/547-2558 or 541/382-8684.

E-mail the author at alton.marsh@aopa.org.

Al Marsh

Alton K. Marsh | AOPA Pilot Senior Editor, AOPA

AOPA Pilot Senior Editor Alton Marsh has been a pilot since 1970 and has an airline transport pilot certificate and instrument and multiengine flight instructor certificates, aerobatic training, and a commercial seaplane certificate.