Issue Number 238
April 1999
A Monthly Safety Bulletin from The Office of the NASA Aviation Safety Reporting System
P.O. Box 189, Moffett Field, CA 94035-0189

GPS GoofsIn recent years, handheld Global Positioning System (GPS) units have become more affordable and more widely used. Many General Aviation (GA) pilots, in particular, find handheld GPS units a convenient supplement to other navigation methods. Mechanical problems with GPS are infrequent; a more common problem reported to ASRS is that old bogy—operator error. A GA reporter illustrates:

Our reporter offers good advice for future GPS familiarization flights. Another GA pilot relied only on the GPS to maintain positional awareness, and found the information deceiving:

Appropriate cross-checking with other navigational aids might also have prevented this pilot’s unauthorized penetration of Class B airspace.

Dead Batteries... and Reckoning
In an effort to get back to his home base, our next reporter passed up a perfectly good VFR airport en route, and then the problems really started to pile up:

Cabin Crew PrioritiesIn spite of what some passengers may believe, the cabin crew’s primary duty is to ensure passenger safety. This duty becomes obvious during an aircraft emergency, when the crew’s skills and training come to the fore, as described in this report to ASRS on an emergency descent and landing:

Flight Attendants receive extensive initial and recurrent safety training just so that all emergency procedures go as smoothly as the ones in this incident did.

Next, cool heads and good crew communications combined to bring an emergency return-to-land incident to a textbook conclusion, as described in this report from a Flight Attendant:

Since the cabin crew provided the Captain with a thorough assessment of the damage, none of the flight crew needed to leave the cockpit to survey the damage personally. All three flight crew members were able to remain in the cockpit and concentrate on preparing for the emergency landing.

Conditional Clearance ConfusionU.S. Air Traffic controllers generally avoid attaching conditions to their taxi instructions. However, "conditional clearances," in which the pilot’s compliance with an instruction is dependent on the completion of an action by an arriving or departing aircraft, are common at many foreign airports. A pilot’s lack of familiarity with conditional clearances can lead to runway transgressions and other problems, as evidenced by this report to ASRS from a military transport pilot flying in a foreign country.

In another incident at a foreign airport, the First Officer of a widebody jet reported a similar misunderstanding of a controller’s conditional clearance.

A final report illustrates how a conditional clearance can be implied in the phraseology of a controller.

Unless the specific conditions of a clearance are explicit and unambiguous, pilots need to query the controller for clarification or for additional information as soon as possible following issuance of the clearance.

Ahoy, Maties!

The Captain of a DeHaviland Dash 8 on approach into an East Coast airport reports a different sort of "conditional clearance":

The reporter recommends that ATC use the phraseology, "Tall vessels in approach area," which is the wording found on both NOS and commercial approach plates. This terminology would likely have triggered recognition among the flight crew that the higher, "conditional" decision altitude was required.

ASRS Recently Issued Alerts On...
Recurring harmonic vibrations in E145s
Model aircraft activity near a New York airport
SF34 engine failure attributed to a leaking oil seal
Two incidents of false door latch warnings on CARJs
False transponder signals from an on-airport aircraft factory
February 1999 Report Intake
 Air Carrier/Air Taxi Pilots
 General Aviation Pilots