# Presentation: 742367

## Circuit City Cessna 560Pueblo, CO February 16, 2005

- Dr. Daniel Bower Aircraft Performance

## Overview

- Types of icing environments- SLD
- Accident aircraft performance
- Cessna 560 modified stall warning system
- De-ice boot activation
- Automatic mode for de-ice boots
- Previous icing recommendations

## Part 25 Appendix CContinuous Maximum

**15****μ**

**40****μ**

- MVD

- 97-99%

**SLD**

- LWC

## Effect of SLD on ice accretion

**Effect of SLD on ice accretion**

**Appendix C**

**SLD**

- Wing leading edge cross section

- Direction of flight

## Rough Ice

- Front Edge of Wing

## Altitude Time History 

**Altitude Time History **

- Clear ice mentioned

- Stall

- De-ice boots operated

- Gray ice mentioned

- PUB

## Accident Airplane Relevant Speeds

**Accident Airplane Relevant Speeds**

- 76

- 81

- 86

- 114

- Clean Stall Speed

- “Ice” Stall Speed

- “Ice” Stick Shaker

- Approach speed in icing

**Accident Stall Speed**

**90**

- Knots

## Accident Sequence

- Airplane slowed below Vapproach
- De-ice boots not operated in second icing layer
- Presence of an estimated 1/6 of an inch or less of ice accreted in SLD conditions caused the airplane to stall prior to stick shaker
- Airplane entered a rapid left roll
- Airplane did not recover in the 1,500 feet agl available

## Stall Warning modifications

- _1996_ - In response to 3 accidents in icing conditions FAA performed flight testing with artificial 1/2-inch ice shapes.
- Ice Shape generated using one App C condition
- Larger droplets not considered
- Resulted in modifications to stall warning system to increase stick shaker speed in icing conditions

## De-ice Boot Operation

- _1998_ – NTSB issued Rec. A-98-91 to activate deice boots upon entering icing conditions
- FAA issued NPRM for several airplanes including the 560.
- Cessna used results from 1996 flight tests with 1/2-inch ice shape to request withdrawal of NPRM
- FAA withdrew NPRM

## De-ice Boot Operation

- Current company and manufacturer guidance states boots should be operated when ice is 1/4- to 1/2-inch thick, and AFM states
- “early activation of the boots may result in ice bridging on the wing”
- _Deice Boot Bridging_ – Ice in the shape of an inflated deice boot forms as the boot is cycled, which cannot be removed by subsequent cycles

## De-Ice Boot Bridging - Recent research

- 1997 Deice Boot Bridging Workshop
- FAA AC 25.1419 (2004)
- Recent research by FAA
**No evidence that modern turbine powered airplanes are at risk for bridging**
- Total number of accidents investigated by the Board related to bridging =

**0**

**Notes:**
However, research performed after the Comair 3272 accident, including the
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1997 Deice Boot Bridging Workshop that included the NTSB, FAA, NASA, airframe and deice boot manufacturers, [CLICK]

Information contained in FAA AC 25.1419, issued in 2004, [CLICK]

And Recent research by FAA all demonstrate that there is [CLICK]

## Automatic boot cycle

- Bridging is no longer a valid reason to allow a buildup between boot cycles
- Research by FAA indicates residual ice is not as detrimental as intercycle ice
- Manually operated boots can lead to excessive intercycle ice buildup in high workload situations

## Revised Icing Certification

- Upgrade aircraft icing certification criteria to include SLD (**A-96-54)**
- Research into effects of in-flight icing, including intercycle and residual ice      (**A-98-92)**
- All de-ice boot aircraft certified for icing should be subject to revised icing criteria

## Summary

**Airplane slowed below approach speed **
**Deice boots were not operated during approach**
**Airplane encountered supercooled large droplets **
- Caused a thin, rough ice accretion with large aerodynamic penalties
**Stall warning was inadequate**
- Ice accretions used to determine the stall warning margin were not representative of the most detrimental

## Summary 

**Deice Boots bridging is not a concern**
- Warrants activation of deice boots upon entering icing conditions
- Warrants development of system for automatically cycling of deice boots
**Icing certification standards**
- Need to be updated based on accident history and recent research, and applied to all deice boot equipped aircraft

## Slide 17